This commit moves payload_builder and the z80_asm code to the data-generator subproject in order to generate the gameboy payloads
at compile time instead of at runtime.
In addition, we select a couple of base payloads (more than 1 for compressibility's sake) and generate binary patches to transform them into
other payloads. We then generate a binary file with both the base payload and binary patches and compress these files with zx0.
This reduces the rom size by about 8 KB.
