Added a test for issue #421
more consistent 4space indent
whitespace
dyslexic typo
Added conversion for RGB+Transparency to RGBA that adds an alpha mask corresponding to the transparency value, fixes #421
Now using the rgbT2rgba conversion for L+transparency to RGBA, dropping the palette hack
Docs: saving RGB+transparency works
Merge pull request #423 from wiredfool/trns-png

Support for PNG tRNS header when converting from RGB->RGBA