Part of #9744
Removes all redundant `# -*- coding: utf-8 -*-` lines from files, as python 3 automatically reads source code as utf-8 now.
`Signed-off-by: Jonathan de Jong <jonathan@automatia.nl>`
* Fix spec compliance; tweaks without values are valid
(default to True, which is only concretely specified for
`highlight`, but it seems only reasonable to generalise)
* Changelog for 7766.
* Add documentation to `tweaks_for_actions`
May as well tidy up when I'm here.
* Add a test for `tweaks_for_actions`
