Minimal changes to get a clean compilation of the SAMD20 Xplained configuration. Still a lot of missing logic

Add configuration for the SAMD20 Xplained Pro board.  Initial check a low-effor, unverified clone of thoe SAM4L Xplained Pro board configuration

More changes to reduce complaints from CppCheck.  Some latent bugs fixes, but probably some new typos introduced

Many changes to reduce complaints from CppCheck.  Several latent bugs fixes, but probably some new typos introduced

Release script no longer tries to keep copies of the ChangeLog and TODO list in the Documentation directory

Add a mouse interface that is similar to the touchscreen interface except that it can handle multple buttons and continuously reports positional data so that it can control a cursor

The USB HID mouse driver is now functional.  There are some usage issues as described in the top-level TODO list