Version 1.1

This is the new STM.
Having the 1-byte header, the compressed data can now be decompressed to part of the screen.

Version 1.0

This is the 'freeze' of version 1.0 - a.k.a. the 'historical' version.
Since the file format at this point doesn't support tilemap width, the whole thing works only for full-screen (or at least full-width) images, unless one provides the info at decode time. This isn't good enough.
Also, the decompressor isn't either interrupt nor VRAM safe.