remove old bundled version of jQuery
remove non-markdown readme
switch to CDN-hosted jQuery (and a much later version too)
editing bugfixes

* add customisable buttons for new arrays as well as new objects or
values
* comment out the .editing class on input fields (TODO: dump it?)
* fix regression where editing property names to empty string wouldn't
delete them
* fix detection of next-array-index when it's 0, as with new arrays