Initialize \pbo for each event

Regression in commit 1f5eb5eb.
Fixes issue #74.
Update version info and changelog
Update README
Fixed headers in profile and test
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.
Don't forget to apply \be to the first/last row/column (again)

The implementation of \be was changed to xy-VSFilter's, which (like
VSFilter's) reads but does not write out the first/last row/column.
Add enough padding for \be to avoid clipping
Use just the necessary amount of padding for any \be value
Calculate \be using [0..64] value range (like VSFilter)

With this, our \be finally closely matches VSFilter's.

The only visible difference is clipping: we add proper padding
and output the whole blurred image, while VSFilter does not add
any padding and hence clips the blurred image too early.
Apply \be after \blur (like VSFilter)
Do the last \be pass using full [0..255] value range
[WIP] Fractional and scaled \be through Dirac deltas and a final box blur