Wave 1

[laerreal]

Next wave of patches from devel.

v2

• add new patches on top to fix SyntaxWarning under Py3.8
• explicitly forbid user to pass window and anchor to CanvasFrame (a new patch, not squashed)
• fixed typos in commit messages and comments
• squashed 'init_submodules_from_cache: update reverted URL in submodule cache "config"'
• dot in 'QemuVersionCache.co_propagate_new_param: clarify docstring'

[laerreal]

v2 is ready