Add ability to select path segments with user defined match; follow on to PRs #146 & #177

[AlainLich]

Hi,
following the approach in previous PRs, this allows to use user defined match.
An example is shown below, more in the README.rst and the tests.

Remarks:

• this uses duck typing for ease of use, yet provides a more classical base class/derived class mechanism for language processors ((older) Pythons, Pypy) that do not support the feature
• extends tests
• this uses recent Python developments, but work-around provided for older/non compliant (yet).
  - https://peps.python.org/pep-0604/#isinstance-and-issubclass
  - https://bugs.python.org/issue44529
  - the duck typing technique requires PEP-0544 features

Examples of code

class Anagram():
                def __init__(self, s):
                    self.ref = "".join(sorted(s))

                def match(self, st):
                    retval = True if "".join(sorted(st)) == self.ref else None
                    return retval

dpath.search(mydict, ['**', Anagram("bella")

Same example not requiring duck typing, appropriate for Pypy (at this time) and older Pythons

class Anagram(DP.types.Basic_StringMatcher):
        def __init__(self, s):
                   self.ref = "".join(sorted(s))

       def match(self, st):
                   retval = True if "".join(sorted(st)) == self.ref else None
                   return retval

dpath.search(mydict, ['**', Anagram("bella")

[AlainLich]

Hi,
this simplifies and cleans up the generalized version that allows for user defined segment matching. It is built over the latest developper commit ( Merge: 2eae6c1 995b7d9, Date: Sat Mar 25 21:07:41 2023 +0300). Tested on Pypy-3.7,-3.9 and several Pythons.

I have 2 PRs:

• Add ability to select path segments using Python re regexprs; follow on to PR#146 & #177 #186 : corresponds to request for restructured, only re.regexp match, replaces Add ability to select path segments using Python re regexprs; follow on to PR#146  #177 that is now obsolete
• this one Add ability to select path segments with user defined match; follow on to PRs #146 & #177 #182: for generalized version. Much simplified from January commits

Tests in workflows:

• (re.regexp only) https://github.com/AlainLich/dpath-python/actions/runs/4651582912
• (generalized) https://github.com/AlainLich/dpath-python/actions/runs/4672219326

I hope this is as expected, also I found that much cleanup/simplification was required from December/January versions.
Regards
Alain