- use clang-format12 or 13 or unversioned executable, only
- check it's actually 12 or 13
- set language standard explicitly to C++17, "Cpp11" is now
  an alias for "latest" which is weird

This change does lead to some thrashing when applying styles,
so I'm not going to do that across the board right now. Changes include:
- extra spaces in lambda-captures
- nicer alignment of lambda-bodies

- duplicate the file to .base
- drop 10-and-later setting that was commented out
- specific setting for lambda-formatting (this seems to be the default)

- Mostly CC0 because they're not interesting
  - formatting, git, travis, transifex
- Some BSD-2-Clause because of habit
  - CMake and shell-script-like files

In clang-format 10, SpaceInEmptyBlock is introduced, and defaults to
true .. which is different from the earlier formatting versions did.
For now, refuse clang-format 10, and search specifically also for
clang-format-9.0.1 because that's what I have on my laptop.

At some point, switch in the config option and then require
clang-format 10 or later (because earlier versions refuse to
run with an unknown config option)

 - don't break after return type in declarations
 - apply same to partition service

 - update the style guide to require braces around blocks
 - add a clang-format file that is pretty close to the
   astyle configuration