misc fixes and "improvements"

[petaflot]

most are details that are pretty "obvious", some are arguable and are justified by the integration of https://github.com/petaflot/pygcode/blob/master/src/pygcode/tools/marlin_parse_MarlinDocumentation.py (does automatic parsing of the documentation to generate some classes) and should not cause any serious trouble.

accept the changes or don't, cherry pick it if you will... I've got enough on my hands not to argue about this. cheers!