This is going to be a bit more comprehensive than anticipated. In order
to cleanly refactor the core and the engine, basically start from
scratch with the implementation.
Goals:
* Test coverage
* Maintain backwards compatibility with module interface as much as
possible (but still make modules easier to code)
* Simplicity
see #23
Hide alias concept for modules in the engine. That way, the individual
modules never get to know about whether a module has been aliased or
not.
see #23
Add controls that allow the user to switch to the next and previous song
in cmus, toggle shuffle and repeat. Pause/play is toggled by clicking on
the song title itself.
fixes#5
Allow the user to use all tags read by cmus (cmus-remote -Q|grep ^tag)
as part of the displayed data (plus the special 'tags' "duration" and
"position").
