It has been required for a while now, and now actually checked in
the makefiles. Before, if you didn't have it installed it would
just recompile everything.
The readme hasn't been updated to reflect this, I think we need
to go through that separately, and see what's really needed. Or
just instruct people to run the batch scripts.
* Add ChibiOS packages to the avr_setup script
* Add git as a dependency
* Rename avr_setup.sh -> install_dependencies.sh
Also fix the Vagrant welcome message to reflect the new directory
structure.