Implemented the American XT computer and the Iskra 3104(A clone made in Belarusian SSR). Also removed the Goldstar 386 & the Unknown Headland 386SX board as they were very buggy and their purpose is now served by the much better Intel 82335 boards.
- 86Box's own headers go to /86box
- munt's public interface goes to /mt32emu
- all slirp headers go to /slirp (might want to consider using only its public inteface)
- single file headers from other projects go in include root
