Create VimPowerline.reset_highlight proxy method

Fixes #411
Merge remote-tracking branch 'zyx-i/fix-411' into develop
vim: Add quickfix window statusline

Closes #419
Update tests
Merge branch 'feature/vim-special-windows' into develop
Update Arch Linux optdepends and conflicts
Merge branch 'fix-archlinux-packages' into develop
vim: Fix missing qf buffer highlighting
Merge branch 'fix-quickfix-buffer-highlighting' into develop
Alter indentation
Make vim and ipython ext configurations optional
Add renderer docstrings.
Remove `pl` argument and first argument to `render*` from docs
Fix documentation for ThreadedSegment classes with @staticmethod’s
Rename PowerlineState to PowerlineLogger
Special-case None priority in place of -1

This extends priorities in both directions, uses slightly faster `is None`
check, makes it consistent with `interval` special-casing also to `None` and
makes lint able to use one simple `.type()` check in place of `.either()` one.
Use different default for functions

This makes it look up `powerline.segments.vim.virtualenv` in addition to
virtualenv in colorscheme like it does with `segment_data`.
Respect segment.py highlight group handling in powerline-lint

Either `highlight_group` or `name` key is enough to determine highlight group
for non-function segments, but powerline-lint requires `highlight_group`.
Move some code from powerline_autodoc to powerline.lib.inspect

To make it available later in lint checker.
Improve arguments checks