SQLite doesn't have an `RLIKE` function, so the query for hashtagged
posts was failing before. This adds a `regexp` function to SQLite and
correctly retrieves all posts on a blog with the requested hashtag.
This closes#55
This adds a new `sqlite` build tag that you should include only if you
want SQLite3 support built in. Both `make run` and `make release` create
builds with SQLite included.