Makefile Improvements

I added 2 things to the Makefile:

First, I noticed that when I only modified header files, things wouldn't recompile.  Now, I have gcc generate makefile stubs that are then included in the main Makefile so that all code dependencies are known to make.  I made the same change for the Libraries Makefile, too.

Second, I added a "debug" target that launches GDB & OpenOCD, then initializes the board to prepare an on-chip debugging session.