Implement new quality mode: full
Update documents
Update tests
Merge branch 'develop' into feature-quality-full

Conflicts:
	config.h.in
Cleanup
Merge branch 'feature-quality-full' into develop

Conflicts:
	converters/img2sixel.c
Merge branch 'develop' of github.com:saitoha/libsixel into develop

Conflicts:
	config.h.in
Merge branch 'feature-quality-full' into develop