MeatPack: Compact only G0-G3 lines.

[hejllukas]

• Only G0-G3 lines have spaces removed. Other lines are stored unchanged, so they are no longer corrupted by the space-reinsertion guessing. Files grow by only about 0.1 %, and less for larger files.
• The no-spaces mode is never switched off, because the firmware shares its lookup table between parallel decoders. Files stay readable by all firmware versions.
• Fixed unbinarize() losing a character when its output buffer grows.