Support IA5 and GSM 7-bit decoding, and fix decoder error while decoding IS-91
Modify value comment to indicate decoder support status
Use bitBuffer in subparameter scope instead of user data scope

In previous code, unsupported subparameter is not handled.
Its data remains in bitBuffer, which should be dropped.
This corrupts following decoding.
By changing scopt of using bitBuffer, unsupported subparameter can be dropped correctly.