Write 'safe' motor library

[x] Separate library arms & legs
[x] legs can't go past max angle
[ ] Optional: Before reaching max angle, danger zone in which only reduced speed and higher force is allowed, to prevent overshooting?
[ ] Optional: Arms can spin multiple revolutions with velocity mode but must then be returned to a trackable position before it's allowed to switch back to position mode
[ ] Arms can start move from nearest full revolution. So if for example it's at 360 and a move starts at 0 and goes to 10, the move now starts at 360 and goes to 370.
[ ] #53
[ ] #52
[ ] By default, stop when force is exceedingly high (suddenly). Overridable by a move.
[x] Homing routine checking with hal sensor

hapiel / Acrobot