ass_utils: don't include freetype headers

They're not even used.
ass_utils: fix declarations

Now they're the same as in ass_utils.h.
Merge pull request #37 from wm4/minor

Minor cosmetics
shaper: rewrite and simplify harfbuzz shaping

Rewrite the core of the harfbuzz shaping function. Gets rid of the
MAX_RUNS limit of runs per line and reuses a single hb_buffer_t,
which should be more efficient.
shaper: use global features correctly

start/end of feature tags is unsigned, so use the proper constant
to signal to HarfBuzz that these features are global. This allows
HarfBuzz to cache shape plans, and that can considerably speed up
shaping, especially if many small runs need to be shaped.
Unroll FNV-1A hash function

Unroll the hash function with Duff's device for improved performance.
Fixed incorrect spelling in copyright notice
Merge pull request #39 from grigorig/shaper-hash-opt

Shaper and hash function optimizations