Add searching/filtering capabilities

[mdippery]

It would be nice to search/filter output. Right now, you can list all comments for a specific subreddit, but that's as fine-grained as the filtering gets. Otherwise, you have to use grep, but this isn't a great solution because grep has no knowledge of the structure of the comments output, so, for example, you can't filter by date or search only the comment bodies for a specific word or phrase.

One idea would be to add a flag that lets you filter/search output using SQL, which would give a lot of control over to the user. In conjunction with #3, I think it could work quite well.