* Remove console output when disabling extension on certain URLs.
* Remove the "loading" ("...") indicator from the badge (it should be
robust enough not to need this, and it should not expose such internal
details to the end-user).
* Only say how long it took to find landmarks when they are (re-)found
as a result of a MutationObserver.
* Make LandmarksFinder.filter() cleaner using map().
* Roll back to deepmerge 1.5.x due to change in behaviour
* Add command definition for main-landmark.
* Add translation text for main-landmark.
* Simplify command handling in background script.
* Make error throwing consistent.
* Remove unused this.currentLandmarkElement() from LandmarksFinder.
* Track which element is the <main>/role="main" element.
* Add this.selectMainElement() to LandmarksFinder.
* Handle the 'main-landmark' message in content.management.js.
* Add info on skipping to the main landmark to the README.
This completes the work started in
f1331fa and closes#106.