GXemul Code2

Minor update for nicer Doxygen output.

Making the counter in the ReferenceCountable class mutable, because const objects also need to be reference countable.

Adding a useful "todo" make target, which greps for all TODO strings in the source code.

Mention the mailing lists and IRC channel in the documentation.

Making the code compile cleanly with GNU C++' -pedantic. The
only module where -pedantic is not used is src/ir/, which needs
to cast e.g. uint8_t* to function pointer (for runtime
generated code).

Updating the TODO.

Adding dummy Save/SaveAs menu entries to the GTKMM UI. Also experimenting with graying out the Undo and Redo actions in the GUI (by querying the ActionStack).

Make StateVariable.cc compile with GNU C++ 3.4.6 without warnings.

Adding some more (dummy) GTKMM menu entries.

Adding a preliminary toolbar to the GTKMM GUI.