ass_strtod: use modern C
build: add more warnings
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>
Append new cache items at the start of the collision list

The idea is that more recently-added cache items are more likely to
get hits.

Signed-off-by: wm4 <wm4@nowhere>
Attempt to make code more readable

No more double pointer dereferencing.
Merge pull request #26 from wm4/warnings

Use more warning flags
Make sure to release each event's vector clip mask

Events with a clip mask but no text such as just
    Dialogue: ...,{\clip(m 47 32 )}
had their clip masks carried over to the next event.

Fixes GitHub issue #22.