Documentation updates.
Adding the new machine and component documentation.
Adding tail.html (for automated documentation creation).
Adding head.html (for automated documentation creation).
Ooops. Forgot to add CommandInterpreter.cc
Ooops. Forgot to add exec_elf.h.
Ooops. Forgot to add mips_cpuregs.h.
Ooops. Forgot to add CommandInterpreter.h.
Merging in _everything_ from the old C++ branch.
Merging in the Command class from the old C++ branch.
