compass and gyrovalues

[Horsevad]

In the AbsoluteIMU class, the methods z_gyro and compass seems to be switched, they are found from line 131 in mindsensors.py

` @Property
def z_gyro(self):
self.mode = 'COMPASS'
return self.value0

@property
def compass(self):
    self.mode = 'GYRO'
    return self.value2`