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>
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.