Debugger for WME

This is a barebones debugger for WME that allows breaking and stepping inside scripts, like the original, dumping vars, like the original, and setting them too.

As far as debuggers go it's a bit of a hack, since we don't have symbol tables and stuff, so we hack around the special II_DBG_LINE instruction; as detailed in a separate document, the next logical step would be to improve on the compiler.