Library is using Asserts without throwing a message

[jposada202020]

Library is using assert statements. It is preferable to add a customary message to inform the problem
outdated: .instead use Exceptions.

Adafruit_CircuitPython_FXOS8700/adafruit_fxos8700.py

Line 98 in fecfb03

assert accel_range in (ACCEL_RANGE_2G, ACCEL_RANGE_4G, ACCEL_RANGE_8G)

[jposada202020]

Fix by #24