use appropriate blitters when mac color depth < 8 bit

[rakslice]

Fixes #2

[rakslice]

There's some issue more than just that; after changing the mode a couple of times it starts to glitch out like there are crazy extra blitters copying stuff to a different wrong place in the same framebuffer, but that is true even for modes that do not need the 8 bit conversion and whose blitter hasn't changed

[rakslice]

But I don't experience that other glitching in the published 1.0.0.05 build, just in all my local builds which are on ndk r26c so it must be to do with that or other changes I made for that

[rakslice]

Ok, that other glitching also happens with the 1.0.0.05 build, I just wasn't trying enough times to reproduce it. I'll take that to a separate issue.