improved avatar gravity code and moved source of gravity vector to main.cpp
Merge remote-tracking branch 'upstream/master'
Merge pull request #201 from Ventrella/master

gravity fixes
if we fail to open SerialInterface twice then don't keep trying
Merge pull request #202 from birarda/master

bail on opening serial after two failed attempts
move SerialInterface constructor to header file
Merge remote-tracking branch 'upstream/master' into domain-rfd