improve and add missing docs
improve and add missing docs

Added the missing `ondestroy` event, updated the docs for the `onremove` event, clarified use of events with use-case examples, moved the `patch` function documentation up with the rest of the API description in the "Usage" section, documented the `key` attribute and when/how to use it, etc.
picodom/picodom,picodom/picodom