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.
Minor refactor as preparation for LayoutResX/Y

Reduces the diff for the next commit. No functional changes.
Implement LayoutResX/LayoutResY

This allows ASS scripts to be independent from video resolution.