Window state tracking is basically the back bond of window fading. We
add a new enum field to the win struct to track the state of the window,
instead of using a set of boolean variables. We also remove the fading
callbacks, since it is only used for fading, so the potential of code
reuse is lost. And it makes the code slightly harder to understand.
Also fixed a problem that --no-fading-openclose is not behaving as
advertised (from my observation, enabling this flag disables fading
entirely, instead of just diabling it for open/close).
Also uses double for opacity everywhere internally. Use opacity_t only
when setting X opacity prop.
TODO: Remove win::*_last
Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>
