Version 1.12 Release candidate 1

1.12 is coming. There are only a few bugs left that I would say are in
scope for 1.12. They are #500, #511, #547, and #584. All related to
Unicode and inconsistant character sizes I think, but I can't reproduce
them.

I won't commit to any timeline on the actual release, but unless I get
some bug reports or help with the above issues in the next week or so,
I'll probably release it.

Changes since v1.12-beta.1:

Fixed:
- general: set specific `IFS` everywhere it is used (#613)
- color: `$LP_COLORMAP` would break if customized with a different sized
  array (a70e80f)
- color: `_lp_color_map()` would return nothing if the passed in value was
  outside the scale range (a70e80f, #455, #499, #604)
- git: changed line check failing if file named "HEAD" existed (#517)
- runtime: when runtime enabled, `$_` would evaluate as
  `_lp_runtime_before` (#451)
- runtime: when running a multipart command line (with pipes or `;`),
  runtime would never show. Now shows runtime of whole pipeline (#614)
- tmux: tmux not showing as multiplexer if custom `$TERM` set (#563)

Thanks to:
* Markus Gebert (@mgeb) for suggested fixes in `_lp_color_map()`
* Tore Anderson (@toreanderson) for suggested fixes and documentation
  around CPU and `_lp_color_map()`
* Daniel Pinyol (@dpinol) for reporting git file named "HEAD" issue
* Alyssa Ross (@alyssais) for reporting CPU and color issue
* Gergo Szonyi (@gex) for reporting `$_` issue
* Joey Liu (@liujoey) for reporing Tmux detection issue
* Nolan Leake (@nolanl) for reporting pipeline runtime issue