The script is taken from bioinfo_utils.

niceload may not be the appropriate way.

Depending on pip version, `pip3.6` sometimes fail with
"ImportError: cannot import name 'main'".

Using `python3.6 -m pip` instead avoids this.

This is not yet fully tested, and may have effects on other pipelines.

It needs a list of identifiers and an annotation file, and generates a
pybedtools.BedTool.

Added function to compute seed disposition from bowtie2 settings.

Also removed some debugging output that was written in a unique file in
/tmp, which prevented the small RNA annotation to be performed by a new
user without erasing this file.

Also made scatterplot axes style more configurable.

Made paired scatterplot plotting function part of libhts as
`plot_paired_scatters`. Modifications in small RNA-seq pipeline not
tested.

Also noticed a problem involving MultiIndex
(https://stackoverflow.com/q/48345640/1878788).

lfcMLE may bring problems with low-expressed genes.

Also:
- Boxplots with labels turned 90 degrees
- do_deseq2 returns size factors