Implement search

Create some cards (they should be inserted into the search index
automatically, now). Then access /api/cards/search?q=search terms to
search for "search terms". Use @name to require that the card's
user_nickname field matches one of the mentioned names, and #tag to
require that the card's tag field matched one of the tags.
Merge pull request #5 from chrisklaiber/master

Implement search