fixed formatting and function naming in bitmask_serial.py.  updated test_encode_decode_bitmask_to_hex().

ran black on bitmask module.  changed the box dtype to int16 and isolated the underflow and overflow tests.

Updated some of the older bitmask functions to allow different option types.  Updated more code to work with Spark bitmask rows.  Fixed an issue with join_bitmask where it was not getting the last interval, added test and updated another.  Added code to convert a EnhancedBitmaskLike to hex.