Using AJAX instead of JSONP can give better caching in the browser, since the
URL doesn't need to contain a (dynamically generated) callback function name.
But because of the same origin policy in JavaScript, AJAX can only be used when
the HTML file is served from the same server as the PGF. The new function
http_get_json in support.js uses AJAX if this is the case, and falls back to
JSONP otherwise.
* Add help button at top of page.
* Change style of word buttons to look like fridge magnets again.
* New options to specify locations of other pages: feedback_url, help_url. If
they are left undefined, no Help/Feedback buttons will be created.
* Shorter test in Google Translate button.
1. The text input field is shown form the start, no need to click.
2. The text input field is removed when no more words can be added to the
sentence.
3. When you press Enter, a word is added to the sentence (1) if there is only
one possible completion left (e.g. if you typed "airp" and the only
completion is "airport"), or (2) if what you typed exactly matches one
of the completions (e.g. if you typed "the" and the completions are
"the", "theatre" and "these").
