Implement temporal queries. (0.2.1a)

Using Nick Galbreath’s snowflake module, OGRe can now convert Tweet IDs
to UTC seconds and vice-versa. This means that Tweets within a given
window of time can be requested by ID. Filtering on kind remains
unimplemented and may not be possible since it looks like Twitter only
allows text posts (images are hosted and attached with a shortened URL).