Wrote separate functions in goes.py for handling exceptions:
check_float64(), check_goessat(), check_photospheric(),
check_date(), check_datetime64(), check_goeslc().
Replaced all occurrences of the exception handling statements
in all functions in goes.py with these functions.
Renamed goes_luminosity() function in goes.py as calc_xraylum()
Changed name of check_float64 in goes.py to check_float() which now
checks if variable is an array of any float dtype: floa64, float32,
or float16.  Calls of this function in other functions in goes.py
have also been changed accordingly.
Ran pylint on goes.py
Fixed bug in check_datetime64() in goes.py by checking test.dtype.type
instead of just test.dtype.  To remain consistent, this was changed
in check_float() too.
goes.py:
calc_rad_loss():
    Fixed bug in Error type when checking observation
times are in chronological order.
goes_lx():
    Fixed typo in calling calc_xraylum() to calculate short channel
luminosity.
    Fixed bug in Error type when checking observation times are in
chronological order.
calc_xraylum():
    Fixed bug in checking whether date keyword was set or was None.
    Fixed bug in determining Sun-Earth distance when date keyword
not set.
time_intervals():
    Fixed bug which caused obstime variable to be set to None after
checking it was of correct type.