We now support 16bit format pixmaps as well as the old ones. Including
both 555 and 565 modes.
We drop the palette argument for pixmap construction as it was only
used for black/white anyway.
Canvas creation is simplified so that there is no separate set_mode
state. Canvases are already created in the right mode and never change.
pixman_region32_t is an efficient well tested region implementation (its
the one used in X) that we already depend on via pixman and use in
some places. No need to have a custom region implementation.
The process loop is responsible for: 1) waiting for events 2) timers 3) events queue for
actions that should be performed in the context of the thread and are pushed from other threads.
The benefits:
1) remove duplicity: till now, there was one implementaion of events loop for the channels and
another one for the main thread.
2) timers can be executed on each thread and not only on the main thread.
3) events can be pushed to each thread and not only to the main thread.
In this commit, only the main thread was modified to use the new process loop.
