Fix Quality 3d returns undocumented values

[jar349]

The documented values for fix_quality_3d are as follows in the snippet below:

Adafruit_CircuitPython_GPS/adafruit_gps.py

Lines 272 to 279 in 41f1596

	self.fix_quality_3d = 0
	"""
	The type of fix for a reading
	| 1 - no fix
	| 2 - 2D fix
	| 3 - 3D fix
	"""

However, the value I am getting for that attribute is 0. If this is an expected value under certain conditions, would you mind updating the documentation to explain? If it is never expected for the value to be 0, could you please explain what I may be doing wrong on my end to receive that value? All other values I am getting look good/correct.

I suspect that the culprit is this block of code:

Adafruit_CircuitPython_GPS/adafruit_gps.py

Lines 634 to 642 in 3e13731

	if data is None or len(data) not in (17, 18):
	return False # Unexpected number of params.
	if len(data) == 17:
	data = _parse_data(_GSA, data)
	else:
	data = _parse_data(_GSA_4_11, data)
	if data is None:
	self.fix_quality_3d = 0
	return False # Params didn't parse

If there's code beyond initializing it to 0 that sets it to 0 - as this block does - then 0 probably does have a semantic meaning that can be documented.