This builds a player to be run from sfxed emulator.

Changing this is not completely supported, but if you really want to do it, it
is possible!

## Build instructions

This requires in your PATH:

* SDCC
* Python 3
* hex2bin; for example [you can use this version](https://github.com/reidrac/ubox-msx-lib/tree/master/tools/hex2bin-2.0)