v1.1.0

Lots of novel implementations, time to bump it up!

• Bug: when user clicks on Preview, local storage gets cleared by mistake. Reported & fixed by @kylesands (see https://www.phpbb.com/customise/db/extension/postlocalstorage/support/topic/246115?p=877342#p877342)
• Added some checks to deal with stale local storage. This is an extreme case when people just happen to completely forget that they still have a message waiting for them for that particular URL. While this is an edge case, it has been pointed out by the validators. Note that old objects (without timestamps) will still be dealt with.
• Save subject field as well as the textarea content (as suggested by @TrekRed).
• Fixed DOM transversal in order to catch text written on a Quick Reply as well (it uses a different class).
• Added a very simple test suite (not on the plugin, just on the GitHub package) with a mock phpBB3 HTML/CSS layout, just to test the actual functionality of the local storage facility. Just point a browser to the local file ./tests/test.html and open the Development Tools on your browser. Debug messages are also sent to the console, if you enable it to see them (regular messages are very sparsely used, while debug messages are chatty).
• Refactored the code to use the 'new' operators ?. and ??, making the overall code much easier to follow & understand (and possibly more bug-proof as well).
• Attempted to add JSDoc documentation on the JavaScript code (still a WIP).