templatekw: factor out showdict() helper Make it less cryptic for common cases.

templatekw: have showlist() take mapping dict with no **kwargs expansion (API) See the previous commit for why. splitlines() does not pass a mapping dict, which would probably mean the legacy template didn't work from the beginning.

templatekw: change _showlist() to take mapping dict with no **kwargs expansion There was a risk that a template keyword could conflict with an argument name (e.g. 'name', 'values', 'plural', etc.) Let's make it less magical.

templatekw: rename 'args' to 'mapping' in showlist() The name 'args' provides no information. Call it 'mapping' as in templater.py.

templatekw: eliminate unnecessary temporary variable 'names' from _showlist() Replace 'names' with the optional argument 'plural'.

color: update the help with the new default The default is now "auto" we update the help to match reality.

upgrade: register all format variants in a list Now that all known format variants exists outside of the function, we can gather them in a lists. This build a single entry point other code can use (current target: extensions). The repository upgrade code is updated to simply use entries from this list. As a side effect this will also allow extensions to register their own format variants, to do this "properly" we should introduce a "registrar" for this category of object. However I prefer to keep this series simple, and that will be adventure for future time.

upgrade: move descriptions and selection logic in individual classes Our goal here is to get top level definition for all the format variants. Having them defined outside of the function enabled other users of that logic. They are two keys components of a format variant: 1) the name and various descriptions of its effect, 2) the code that checks if the repo is using this variant and if the config enables it. That second items make us pick a class-based approach, since different variants requires different code (even if in practice, many can reuse the same logic). Each variants define its own class that is then used like a singleton. The class-based approach also clarify the definitions part a bit since each are simple assignment in an indented block. The 'fromdefault' and 'fromconfig' are respectively replaced by a class attribute and a method to be called at the one place where "fromconfig" matters. Overall, they are many viable approach for this, but this is the one I picked.

upgrade: introduce a 'formatvariant' class The 'deficiency' type has multiple specificities. We create a dedicated class to host them. More logic will be added incrementally in future changesets.

upgrade: implement '__hash__' on 'improvement' class The pythonomicon request its implementation.