Add python_test, more exclusions

Fixes #289
Fix git/hg repo tests
Fix license

Fixes #299
Add python-argparse dependency
Merge branch 'improved-ebuild' into develop
Renamed term_24bit_colors to term_truecolor
Make @window_cached use @wraps

Otherwise documentation is not saved (hidden in decorated function only visible
in the closure).
Move add_local_theme and get_theme to vim renderer

In any case for all other extensions they are useless. (Except for ipython, but
it is TODO and I am not going to use matchers this way, simple dictionary
lookup is better in this case.)
Remove unused “colors” key
Add highlight group data for powerline-lint
Fix highlight group documentation for line_percent
Make some functions be more convenient for use in lint checker
Add JSON parser producing marked values

Ref #278
Add most configuration checks

Changes:

- Add main configuration, colors.json, almost full themes and colorschemes
  checks
- Make powerline.lint.check return whether it had problems
- Make powerline-lint fail if .check reported problems
- Make tests run powerline-lint
- Add the script to the list of the installed scripts

Fixes #278
Make parser less restrictive and able to report problems
Some changes to make it work in non-python2.7
Some fixes for flake8
Rename YAMLError to JSONError and MarkedYAMLError to MarkedError
Make Reader also produce MarkedError, remove JSONError
Make lint more error-prone

Target: report as much errors as possible in a single run without failure