Merge bitmaps before creating ASS_Images; introduce x86 ASM.
This is a large set of changes, originally tracked at 11rcombs/noucome-proof.
Allocate track array exponentially

This reduces the frequency of reallocations.
Remove some ass_msg() calls

These aren't very useful for debugging due to the high volume of the log
output in problem cases. In fact, all they do is making the code slower
(the message callback can easily appear in the profiler output, even if
the callback doesn't actually print the messages).
fontconfig: don't compact the sorted font list

Some broken fonts are dropped by Fontconfig during compacting.
Simplify hash function

We can rely on fast multiplication and good compilers.

v2: use default FNV-1a prime

Signed-off-by: wm4 <wm4@nowhere>
Signed-off-by: Grigori Goronzy <greg@chown.ath.cx>
Attempt to make code more readable

No more double pointer dereferencing.
ass_strtod: use modern C
build: add more warnings
Fixed post-rebase issues