Log Message:
libass: updated to 0.15.0

Release 0.15.0

Boo! Three long years in the making due to large internal changes, this \ 
long-awaited release brings bug fixes, speed, and a new mechanism for opting \ 
into VSFilter-incompatible features:

Fix backwards/VSFilter-incompatible font sizes with FreeType 2.10+
Improve speed via better caching
Require HarfBuzz unconditionally to ensure good shaping for complex scripts
ass_set_use_margins(true) now simply places text on the whole screen instead of \ 
attempting to tie it to video positioning (set by the margin values) and failing \ 
in various ways when margins are used to implement pan & scan in a video \ 
player
Add ass_track_set_feature() & catch-all ASS_FEATURE_INCOMPATIBLE_EXTENSIONS
Add ASS_FEATURE_BIDI_BRACKETS to enable Unicode 6.3+ bracket matching when \ 
applying the Unicode Bidirectional Algorithm (incompatible with VSFilter; \ 
requires libass built with FriBidi 1.0+)
Fix stack overflow on deeply nested \t tags
Fix positioning of events with leading line breaks
Fix small but nonzero \bord becoming \bord0 (regression in 0.14.0)
Measure BorderStyle=4 box padding from glyph border, not from glyph fill
Scale everything from script resolution if storage size is not set (including \ 
borders and shadows regardless of ScaledBorderAndShadow)
Fix the default aspect ratio calculation when neither ass_set_pixel_aspect() nor \ 
ass_set_aspect_ratio() is called
Multiple fixes for karaoke override tags
Handle memory allocation failures better: avoid some crashes and produce images \ 
closer to truth
Avoid some integer overflows
Add internal infrastructure for regression testing
Improve VSFilter compatibility:
- Treat invalid nested \t tags like VSFilter
- Make \t(T,T,...) at time exactly T use the post-transition values
- Make lines stack more like they do in VSFilter
- Default ScaledBorderAndShadow to 0 (like VSFilter), except for subtitles that \ 
were produced by old FFmpeg/Libav
- Make shadow positioning with 3D transforms match VSFilter’s
- Cut out glyphs from border & shadow in all the same cases as VSFilter
- Match VSFilter on animated color tags with negative acceleration
- Fix parsing of some files that VSFilter accepts but libass didn’t by \ 
ignoring leading whitespace in each line of an ASS file or CodecPrivate
- Improve font selection with CoreText
- Stop faux-bolding fonts that are too bold to get faux bold in VSFilter
- Ignore leading/trailing spaces when calculating height of nonblank lines
- Match VSFilter on \fade with large alpha value arguments
- Stop splitting bitmaps on font substitution
- Multiple fixes for Banner and Scroll effects
- Multiple fixes for karaoke override tags