Substitute documentation to reference AvrGcc by default, which locks gcc
to the dependency folder.
AnyAvrGcc is inteded to use any system/external gcc version (as the name
implies).
Remove fixed version in AnyAvrGcc.cmake
Update build.py to use current avr-gcc version defined in bootstrap.py
Attempt to change MM-control-01.hex to MMU2SR-<project version> like in buddy releases