Make a plugin-architectured ConfigFilesStore and make it default local store

[thorwhalen]

The work is really done in the wrapper that will be used on TextFiles (but can be reused elsewhere).

The wrapper uses wrap_kvs with postget argument.

The postget is a class or function that uses the usual "register" means to register new rules.

The default rules include extension-based conditionals for all things that can be handled by builtins (ini, cfg, csv, tsv, txt, ...) as well as for those that need (e.g. xls), or might need depending on the python version (e.g. toml and yaml) a third party. In the case of the third party need (or might need), the imports are "protected" in the functions or contextlib.supress and helpful error messages are given to the user dynamically.

Before starting the task, search for tools that already exist in config2py as well as review the following modules, which may help out a lot:

• pyckup/base.py:grab

... and older ones (that may, or may not, have been already absorbed in the grab function of pyckup):

• dol/misc.py
• py2tore/access.py
• py2store/my/grabber.py