Implement trivial ROM compression

[kbeckmann]

This is mostly useful for tiny homebrew ROMs, but might be useful for users who use the Pico which only has 2MB of flash.

Idea:

Python script that chops up the file into 4k blocks, generate a table that points to the right block, write the mapping in c code done

[kbeckmann]

This is implemented now and seems to work well.