Only check that all colorschemes have theme, but not the opposite
Implement theme hierarchy

Fixes #783
Move all unicode characters from themes to powerline.json
Make now_playing segment accept state symbols from arguments
Implement single-level merging of “args” dictionaries
Copy a number of unicode values to powerline.json
Allow checking NowPlayingSegment
Use more precise error messages in test_tabline.vim
Add ASCII-only theme
Use ascii theme in local overrides
Add unicode-only theme
Add unicode_terminus top-level theme

This one contains only glyphs present in terminus font.
Add unicode_terminus_condensed theme
Add description of shipped themes to documentation
Fix labels in configuration/reference.rst
Refactor powerline.lint.inspect: do not special-case *ThreadedSegment

Fixes now_playing segment handling in python-3.4
Merge pull request #958 from ZyX-I/theme-hierarchy

Implement theme hierarchy