Add reference notations of ImageMagick
Minor fix
Add welsh resampling filter
Catch unhandled errors
Implement --quality option
Minor fix
Handle some out of memory errors
Update README
Minor fix
Update manpage
Merge branch 'feature-quality-option' into develop

Conflicts:
	converters/quant.c
Merge branch 'welsh-filter' into develop

Conflicts:
	README.md
	converters/img2sixel.1
	converters/img2sixel.c
Use pattern dither when doing monochrome quantization
Add license file of arakiken's tw
Add tw license notice to README
Update manpage
Merge branch 'feature-pattern-dither' into develop
Update version