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.
Merging in the Checksum class from the old C++ branch.
Updating the TODO.
Merging Action and ActionStack from the old C++ experimental branch.
Merging in the (dummy) native code generation classes from the old C++ experiment.
Adding a link to the release notes from the main documentation index.
