Merge branch 'release-0.19'
Merge branch 'develop'
Merge branch 'release-0.19'
Add PNM loader imported from kmiya's sixel
Enable pnm format loader in loader.c
Minor fix
Build with frompnm.c
Don't use stbi_load_from_file
Add functions detect pnm/sixel image format
Do not use stbi loader if image format is pnm/sixel
Minor fix
Merge branch 'fix-segfault-without-arguments' into develop
Merge branch 'release-0.19'
Merge branch 'master' into develop
Merge branch 'develop' into stbi-stub
Minor fix
Minor fix
Merge branch 'feature-load-ppm' into sandbox
Merge branch 'stbi-stub' into sandbox

Conflicts:
	converters/loader.c
Minor fix