Type converter signature should be changed (or extended)

[jenisys]

The type converter function signature should be changed to:

def type_converter(text, match=None, match_start=0):
    # -- NEW: match_start : int = 0, 
    # refers to the first group in the match object for a field where the converter is used.
    pass

This change would allow to provide a generic Parser without type knowledge.
In addition, user-defined types should also provide this signature. Currently, only the first parameter is supported there which prevents to use complexes type converter cases.

Due to backward compatibility reasons, the old user-defined signature should be supported, too, at least for some time.

[moi90]

Yes, it would be great if one were able to access the re.Match object to extract individual groups, for example!

@r1chardj0n3s, @wimglenn, do you think this would be feasible? I could be able to provide a PR.

@jenisys: What is the motivation for match_start?