Add a (breaking) test to verify that the document’s title is updated on navigation

A touch of TDD: Add a test for a piece of functionality before writing the code to make that test pass
Add logic to update <title> on navigation, to pass our breaking test

Parse the responseText with a regular expression to identify a <title> element,
then set the document.title to the matched string.
Merge pull request #4 from kadamwhite/ajax-loading

Update the <title> element when loading new images via AJAX