Each widget can now return a state using the method "state()". This
string is then used to look up a theme information which is used instead
of the default or module theme, if found.
see #23
Add customized separators:
* The default separators are automatically disabled if custom separators
are used (to "just" disable the default, use empty custom separators)
* Use previous background color as their background color and the
current background color as foreground color
* Allow the separator-block-width to be configured
see #23
Allow sub-themes ("iconsets") to be merged into the "main" theme. That
way, effectively, it's possible to define colors and icons in separate
JSON files.
see #23
