Merge pull request #11 from ahcorde/master

ALT_HOLD mode (take off and land)
Merge pull request #12 from ahcorde/master

ALT_HOLD (take off and land)
Testing the mode "Altitude hold". Different altitudes
GPS not connected
Take off -> stabilize mode
Land -> altitude hold mode
good IMUs
good landing
antivibration platform
Altitude issues
Merge pull request #13 from ahcorde/master

Testing the mode "Altitude hold". Different altitudes
Testing LAND mode
GPS not connected
Take off -> altitude hold mode
Land -> altitude hold mode
good IMUs
good landing
antivibration platform
Altitude issues
Merge pull request #14 from ahcorde/master

Testing LAND mode
servo signal issues
Merge pull request #15 from ahcorde/master

servo signal issues
LOITER + RTL
GPS issues
Change mode - ALT_HOLD, LOITER and RTL