Implement animations

Squashed all the stuff:

init

Update README.md

options

performance

Animation no longer jumps if started in the middle of an animation

Doubled default transition length

Minor bugfix, preformance

Track x and y separately to aviod jumping in mid-animation repositioning

Added video to readme

docs

docs

fixed graphical glitch with non-transparent windows

now animates window scaling too (but only if the window grows)

added options for size transitions

and actually respect the new options..

and actually respect the new options..

added center-spawn option

added center-spawn-screen option

fixed center spawn

added no-scale-down

goofed

remember old windows

remember old windows

docs

fixed shadow

fixed shadow

fixed shadow

fixed shadow

lost no-scale-down due to revert

lost spawn-center due to revert

Fixed #2

fix missing window borders

src/common.h

@@ -527,3 +527,8 @@ static inline void wintype_arr_enable(bool arr[]) {
 		arr[i] = true;
 	}
 }
+
+/**
+ * Get current system clock in milliseconds.
+ */
+int64_t get_time_ms(void);