Filter By Tag

I added this code before I found the "--always-display-tags" switch which allows for useful grepping. I don't know if it's useful, but thought I would pass it along anyways.
@JakeWharton I created a new PR (#68) that contains the changes from the new repo. If we still want the changes, we can either merge that one, or merge this one as-is and I can address the comments in another commit.