Add data gathering for the configured default namespace of the current
kubectl context. Display that data as a string directly after the
context string, separated by a colon.

While this is a separate chunk of data from the context, it is actually
part of the context definition, and so it makes sense to display it
along with the context.

While most Kubernetes objects are subject to the strict DNS name
restrictions, kubectl contexts never have their name server-side, and so
do not have the same restrictions. This means a context name can include
any characters, meaning we have no safe way to parse it out of a data
string. I wanted to use:

line=$(kubectl config view --minify --output 'jsonpath={.current-context}{" "}{..namespace}')
IFS=' ' read kubernetes_context kubernetes_namespace <<<"$line"

But since spaces can be in a context name, this would break.

Extension to #496 to add [AWS Vault](https://github.com/99designs/aws-vault)
support. AWS Vault does not set the AWS_PROFILE/AWS_DEFAULT_PROFILE
variables, but does add AWS_VAULT. Since this is philosophically the
same as showing an AWS profile on the prompt, I simply added AWS_VAULT
to the detection chain.

LP_KUBECONTEXT_DELIMITER_SUFFIX removes a suffix (dev-cluster and - becomes ->
dev). But sometimes the boilerplate part is a prefix, as when using AWS
EKS (Elastic Kubernetes Service).

`aws eks update-kubeconfig --name $CLUSTER_NAME` sets the cluster's ARN
as the context name, most of which is boilerplate:
`arn:aws:eks:$REGION:$ACCOUNT_ID:cluster/$CLUSTER_NAME`.

Rarely, sensors or acpi can return no temperature data. In this case,
the data function would return false and 0, but the detect function
would error if set -u was enabled.

Harden all of the four temperature functions against this, and greatly
increase the test coverage to cover these four functions, as well as
adding a specific case for the tools returning no data.

This also allows for the temperature functions to return values less
than 0, if somehow a device has all temp sensors returning less than
that.

Mention in the function documentation that it is possible for the
function to return a not set string.

Fixes 670

Fixes https://github.com/nojhan/liquidprompt/issues/600.

Fixes: https://github.com/nojhan/liquidprompt/issues/249

The problem is simple enough: the extra backslashes or percents that
__lp_escape() adds show up in the title, as the title is changed in the
previous commit to no longer be printed as part of PS1. The fix is not
so simple.

This patch adds "raw" copy of the data strings for username, hostname,
and current path with no color or shell character escaping. This is
designed for putting into the terminal title, but it could also be used
for comparisons. lp_path_format() already had a no formatting return var
in lp_path, but now it is not shell escaped.

The title is changed from duplicating the prompt to instead showing just
the core bits in the central brackets: username, hostname, current path,
followed by the prompt mark. As well as the user prefix, postfix, and
MARK_PREFIX. This is a change from the long standing default, but it is
customizable both by themes and users, and I have long seen complaints
of the current title layout being less than helpful.

There is one small issue though: to prevent LP_PS1_PREFIX,
LP_PS1_POSTFIX, and LP_MARK_PREFIX that have color from messing up the
title, the whole title string is still passed into lp_formatted_title()
to strip color out. This is less than ideal, but faster than treating
those 3 variables by themselves.

Again further work on #651. This time it is simple: both Bash and Zsh
set the exact same hostname that they use for their prompt escape
sequences into HOSTNAME and HOST, respectively.

Then it is a simple matter to replicate their "short" version by
truncating the string to the first period.

Another replacement for #651, this one was mostly simple. Unfortunately,
not all shells set an environment variable for user. Zsh always sets
USERNAME, but neither Bash nor Zsh set USER. login(1) does however, so
it _should_ always be set. See https://unix.stackexchange.com/a/76356/421569
for some good info.

Fall back to id -nu just in case the variables don't work. I don't know
how portable that command is, but since it is a backup, it should be
fine.

By calling date(1), another shell prompt escape sequence is removed.
This also allows for custom formatting strings.
Add and update docs for time functions.

Resolves #281

This will add `[profile_name]` to the prompt should it find either
`AWS_PROFILE` or `AWS_DEFAULT_PROFILE` set in the environment.

This is useful when switching between different AWS profiles and
working with multiple accounts.

Add a data source to get the current Kubernetes context. Includes a
mechanism for truncating the context to the first matching character,
configurable.

The data source is disabled by default. The truncation is also disabled
by default (disabled by setting the config option to the empty string).

Add a default theme function to format the context like the other
development environments.

While most OSs do have a 5 minute data point of load average, most have
1 minute as the shortest, which is what Liquidprompt uses.

The load average display has been notoriously not helpful. It is scaled
by the CPU count, and then multiplied by 100 to make it apear like a
percentage. But load average and CPU utilization have almost nothing to
do with each other.

This change displays the actual load average, while keeping the
threshold and color calculations the same. This means the functionality
is no different, just that the display has changed formats.

To make the configuration options LP_LOAD_THRESHOLD less confusing, it
too has been changed to be an actual load value, no longer "centiload".
Old values are still supported, which is done by checking for a period
('.') in the string. So for this historical reason, all new values must
have a period in them. Which should not be a problem, any useful value
would be a float.

Change the greater-than comparison to a greater-than-or-equal-to, since
it is a little more intuitive to what would be expected from the config
option.

Since I was at it, I added a new config option LP_LOAD_CAP, to configure
the range for color values output by _lp_color_map() for load averages.
It too takes a load average float value. As it does not have the
historical reason above, it does not accept "centiload" values.

The implementation details are long. Floating point math does not exist
in shells (which I suspect is the reason that "centiload" was used in
the first place). To make it possible to compare, the values are scaled
up by 100 just like before. They are not shown to the user. 100 scaling
should be plenty for the precision we need.

To do the scaling, __lp_floating_scale() is added, which as a standalone
function, can be unit tested.

And for good measure, the lp_load return value is passed through
__lp_escape(), just in case.

Special thanks to Tore Anderson (@toreanderson) for helping dig through
the issues here.

This data source already existed, but only as part of the default theme
activation. I doubt that many other themes would want to include it, as
it was not even part of the default theme by default. It was only a
optional template section that I doubt many used.

But by breaking it into a function, we can unit test it with test cases.

A few of these typos are really abbreviations that shouldn't have been
abbreviated. But most of them are stupid mistakes.

Co-authored-by: Mark Vander Stel <mvndrstl@gmail.com>

Add full documentation of Liquidprompt as Sphinx documentation written
in reStructuredText.
Add a ReadTheDocs config file, as that is where this documentation will
be hosted.

This documentation took a long time to write. And I'm sure it's not
completely done yet, but I need to get something in the history.
I am mostly confident that the current state of Liquidprompt is well
documented now.