v3.4.0 - Menus

• Add miru.ext.menu, which aims to make creating complex, nested menus easy. See the documentation & example on how to use it.
• Overhaul View autodefer logic. ViewContext are now automatically deferred if a response is not issued within 2 seconds, even if the callback is still running.
• Add ItemHandler.get_item_by() and ItemHandler.get_item_by_id().
• Deprecate ModalContext.get_value_by_predicate in favour of ModalContext.get_value_by. It will be removed in the next minor release (3.5.0).
• Large amounts of typing improvements across the library.
• Add CONTRIBUTING.md and configuration for common editors for better contributor experience.