Add rle24rlecut and rle24rletrns similar to the rle8 and rle4 variants

[brianpopow]

@jsummers First of all thank you for creating this bmpsuite, it was very helpful for me!

I think it would make sense to add two additional bitmaps for RLE24, which use “delta” codes, and early EOL & EOBMP.

[jsummers]

Thanks for the idea, but I'm leaning toward declining it, at least for now. RGB24 is a rare and obsolete feature, and the suite usually only has one testcase for such things.

[brianpopow]

ok, i understand.