Add BBC Micro Core

[nattthebear]

• https://github.com/scarybeasts/beebjit - Probably simple to port, but low on features
• http://www.mkw.me.uk/beebem/index.html - One of the more popular more featureful emulators
• https://github.com/stardot/b-em - Another very popular emulator
• http://modelb.bbcmicro.com/index.html - last update was in 2013, and it was only to say that the latest build from 2004 still works ¯\_(ツ)_/¯