Better ASS parsing, part 1
Better ASS parsing, part 2

Ported old code to new API
Removed unused code
Some bugfixes
Fixed font matching

It now tries to match exact font (with same bold and italic parameters)
and fallbacks to regular if it wasn't found.
Fixed ass parsing

Dictionary didn't like mutable hash elements
Better test coverage. Some bugfixes.

Also, we don't process useless blocks anymore. They're useless anyway.