create a more compressed disk format

[mainroach]

*Take advantage of VLC for block indexes.
*add a 2nd layer for per-scanline palettes. (One bit at start of scanline to denote of its palette or inline)

[mainroach]

Note, after some tests, the entropy-minimal frames data is about 50% what the final output size is; however VLCs are only allowing about 25% savings since it requires complex trees and codeword mappings to be part of the stream.