[WIP DNM] Replace build scripts with a Makefile

This is a proof of concept. It's working pretty well I think (!),
but it's not finished, (hence do not merge).

Ideally all of the .sh and .cmd files can be replaced.

Todo:
- For windows users, have to sort out how to run del /p vs rm -rf
  and etc
- Need to test on windows also (I can't do it)
- Convert the other build scripts not yet done