Initial check-in of the MIPS simulator. Work still needs to be done on

Initial check-in of the MIPS simulator. Work still needs to be done on
the run-time support code (interp.c) to provide better tracing, and
also to add profiling and architecture specific support. At the moment
the simulator has a fixed size, fixed address memory area, and
simulates a subset of the IDT monitor calls (enough to execute test
programs).

The other major feature (could even be a bug) is that the simulator
makes use of the GCC "long long" extension. Work has been started to
make this a build configuration option... but there is still a lot of
this to be done.