start work on #33

add giflib source and include it binding.gyp
progress writing a gif decoder
done with gif decoding function
update readme
Merge branch 'version/0.0.6' into feature/gif
add gif decoding tests
gif encoder (seemingly) done (without transparency). it compiles.
preliminary gif encoding works
allow gif colors table any arbitrary number of colors up to 256
progress with gif encoder transparency
can generate gif
use local color table instead of global
can encode transparent gifs. can define dynamic transparency threshold.
fix a gif decoder bug

if a gif was decoded and the image had no graphics extension, it was
treated as an error. it's not an error, because graphic extension blocks
are optional.
add tests and examples for gif encoding/decoding
update readme with gif
clean up gif dependencies
bring back gifalloc.c dependency
Merge branch 'feature/gif' into version/0.0.6

Conflicts:
	tests/02.operations/001.open.js