Add an at-symbol to provide hinting at desired contents.

While it doesn't matter because Twitter can handle an at-symbol in the
URL, it's not really desirable to expose at-symbols in the URL,
  especially since they're being emailed to users.
Merge pull request #16 from ltw/at-symbol-design

Add an at-symbol to provide hinting at desired contents. <3 @ltw
Bring back duration!
Merge branch 'master' into fix_failing_specs