Add an optional C-implementation for configmix.config.unquote and configmix.config.pathstr2path. This is currently for Python 3.5+. It is tested with Python 3.7 and Python3.8 (FreeBSD 12.2 amd64, LLVM 10.0.1). A build for the stable API ("abi3") fails because PyUnicode_New() is currently not in the stable API. Also includes are extended tests for unquote() and pathstr2path().

# -*- coding: utf-8; mode: yaml; indent-tabs-mode: nil; -*-
#
# Part of deletion check
#
%YAML 1.1
---

db:
  user:
    name: '{{::DEL::}}'

test:
  Str: '{{::DEL::}}'


to-be-deleted-but-reassigned: 'the last value'