Execute content script only in the topmost frame

This disables form filling in iframes.
Fix issue with poorly commented code
Update to 0.2

Makefile: add uninstall target
Makefile: install manifest.json in correct path
popup: add "add key" mock-up UI
README.md: document alternative install process
Prep all for user installation
build.yml: install himitsu first
popup.js: don't hide host pair
Add XPI to makefile and .build.yml
Remove extraneous log statements
Rig up autofill with new popup UI
popup: tweak UI for single key
Add initial disambiguation dialog
native: handle client::next errors
native: refactor out dispatch code

Fixes: https://todo.sr.ht/~sircmpwn/himitsu/29
icons/lock-512.png: recolor
Implement basic himitsu usage
Decode himitsu keys in native messenger

Saves me from doing the work in JavaScript