Minor optimization: cache jQuery element inside loop
Set the 'title' attribute of the timeago element to be the text from the element.

(Only happens the first time we wipe the original text, and only if a
'title' wasn't already set).

This allows your original HTML (before JS runs) to have a human readable date like
"April 11, 2014" and then have smart-time-ago make it say "1 month ago"
but then the user can still hover their mouse to see the more detailed/accurate
format of the date.
<time class="timeago" datetime="2014-04-11">April 11, 2014</time>

Of course, a tooltip could be done already without these changes if you make the
original HTML like this:
<time class="timeago" datetime="2014-04-11" title="April 11, 2014">April 11, 2014</time>
However having the 'title' before the text has changed is redundant, and not in the
spirit of JS gracefully enhancing the page.
Minor simplification of the setInterval
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