Fix premature parser exit on }{ in drawing mode

Fixes #75.
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.
unistd.h is not needed
Move ASS_Shaper declaration to ass_shaper.h
Explicitly include ass_utils.h everywhere (and not config.h)
Fully fix compilation with MSVC/ICL

As before, this does not add any build system support:
a config.h file and a project must still be manually created
(or the compiler can be run manually instead of using a project).