Alpha Support

[WaldemarLehner]

I was wondering if there are any plans on adding support for an alpha channel

[LuizZak]

I've thought about it since another issue where someone brought it up. I've refrained from adding alpha channel initially because I knew for sure I'd get it wrong and then we'd be stuck with some alpha channel implementation that wasn't correct or didn't work when using pre-multiplied bitmaps or something like that.

I'm open to suggestions related to alpha channel, but still I think it'd be hard to get it right (and fast!) on the first try.