IMUPLUS_MODE and M4G_MODE not properly supported.

[ViennaMike]

Per the documentation for the BNO055 (section 3.3.3) there are absolute and non-absolute (relative) fusion modes. All 5 of these provide meaningful Euler angle and quaternion outputs, but the code in adafrit_bno055.py does not include IMUPLUS or M4G modes in the mode list to return values and instead always return None's.

Fix needed:
In the code:

@property
def euler(self):
    """Gives the calculated orientation angles, in degrees.
    Returns an empty tuple of length 3 when this property has been disabled by the current mode.
    """
    if self.mode in [0x09, 0x0B, 0x0C]:
        return self._euler
    return (None, None, None)

the values 0x08 and 0x0A need to be added to the list.
The same two values need to be added to the list in:

@property
def quaternion(self):
    """Gives the calculated orientation as a quaternion.
    Returns an empty tuple of length 3 when this property has been disabled by the current mode.
    """
    if self.mode in [0x09, 0x0B, 0x0C, 0x08, 0x0A]:
        return self._quaternion
    return (None, None, None, None)

[ViennaMike]

I've submitted a pull request that fixes this problem (and three similar ones I discovered while comparing outputs to what they should be, per the data sheet, for each mode).

I got a "failure test" on the request, but the only issues I see listed are issues with existing code I didn't touch. If I need to fix something, let me know what needs to be done.

[ViennaMike]

Fixed by pull request #76.