optional compile time dependency. This means the former code paths are
all retained and new ones are wrapped in #if HAVE_LIBSFDO. Behavior
should be identical now between the two code paths. Later commits will
add the handling of icons specified as absolute paths which both former
swaybar code and libsfdo have thus far avoided.
* The loop functions are now prefixed with `loop_`.
* It is now easy to add timers to the loop.
* Timers are implemented using pollfd and timerfd, rather than manually
checking them when any other event happens to arrive.
This starts up the event loop and wayland display and shims out the
basic top level rendering concepts. Also includes some changes to
incorporate pango into the 1.x codebase properly.
