[HarfBuzz] harfbuzz: Changes to 'accelerate-lookups'

[Behdad Esfahbod]

New branch 'accelerate-lookups' available with the following commits:
commit cdbf24e87f0d8eaf16a733a293b71bc043fb79c7
Author: Behdad Esfahbod <behdad at behdad.org>
Date:   Mon Apr 29 21:16:15 2013 -0400

    [OTLayout] Accelerate lookups by batching
    
    If we need to apply many many lookups, we can fasten that up by applying
    them in batches.  For each batch we keep the union of the coverage of
    the lookups participating.  We can then skip glyph ranges that do NOT
    participate in any lookup in the batch.  The batch partition is
    determined optimally by a mathematical probability model on the glyphs
    and a dynamic-program to optimize the partition.
    
    The net effect is 30% speedup on Amiri.  the downside is more memory
    consuption as each batch will keep an hb_set_t of its coverage.
    
    I'm not yet convinced that the tradeoff is worth pursuing.  I'm trying
    to find out ways to optimized this more, with less memory overhead.
    
    This work also ignores the number of subtables per lookup.  That may
    prove to be very important for the performance numbers from here on.

commit 68db8c49d8e4a49a260b8260e24a604c5fdc0458
Author: Behdad Esfahbod <behdad at behdad.org>
Date:   Sun Apr 21 16:03:27 2013 -0400

    [OTLayout] Add start/end to apply_string()
    
    No functional change.

commit 1b972d893a5066a988833e9a6699e06cbf132d9c
Author: Behdad Esfahbod <behdad at behdad.org>
Date:   Wed Apr 24 16:42:05 2013 -0400

    [OTLayout] Add is_inplace() method to GSUB

commit 07034f447bc33bec945629a23b3a2dfc073deeca
Author: Behdad Esfahbod <behdad at behdad.org>
Date:   Sun Apr 21 16:34:18 2013 -0400

    [API] Add hb_ot_layout_lookup_get_coverage()