Added User Settings item to Tools/context menus.
PEP8 naming says to use self, even with class methods.
PEP8 naming
on_new and on_activated are always called after on_load, so no need for on_load or to call on_activated from on_new.
Added flake8 config.
New methods to deal with common case of creating options from settings for passing to a linting method.
Make sure that error marks override identical warning marks.