Implement fast quad-tree rasterizer in C and x86/SSE2/AVX2

Signed-off-by: Rodger Combs <rodger.combs@gmail.com>
Fix corner case: \move with identical start and end times
mystrtoll: don't truncate to int
Make \be animatable

VSFilter has supported this since version 2.39.

Use the raw floating-point value of the \be argument in the animation
formula, like xy-VSFilter has done since version 3.0.0.45 (404301a3).
Reset clipping mode on every rectangle \clip

Prior to this fix, both of the following:
    \iclip(0,0,9999,9999)\clip(0,0,9999,9999)
    \iclip(0,0,0,0)\clip(0,0,9999,9999)
hid the whole picture in libass. The correct behavior
in both cases is to display the whole picture.
Fix \1a, \2a, \3a, \4a with invalid argument

Reset to the initial color's alpha component, not red.
[WIP] Parse override tag arguments exactly like VSFilter