Massive re-work update, as discussed.

[waltje]

Many changes in the whole project, but mostly:

• re-establish Windows and Linux as primary targets, hopefully you can fix up the OSX one.
• split up the BASIC module for better structure
• added several missing functions, variables and statements
• prepared for adding "screen" (using Ncurses) support
• prepared for adding "file I/O" support

Still a lot of work to be done, but at least it's working again :)