Optimize encoding to sixel sequence.
(http://mlterm.sf.net/optimize-sixel.png)
Add -E, --encode-policy mode.
Fix help message.
Merge pull request #16 from saitoha/arakiken

Optimize encoding to sixel sequence.
Merge branch 'develop' of github.com:saitoha/libsixel into develop
Add the explanation of -E option to manpage
Merge branch 'develop' into feature-builtin-palette

Conflicts:
	converters/img2sixel.c