remove duplicate call to Twitter.users

I think this was a bug. It looks like previously this fetched the users,
then the following loop ALSO fetched the users (the correct way). So,
just combine the ids here.
add Rack logging for easier access to the logger
ignore .rvmrc
added caching to all Twitter API calls

Added dalli caching library. Cached response from friend_ids, so that
subsequent "fights" that had at least 1 person in common would not have
to go to Twitter. Cached individual users by both their id and handle.
Continued using the bulk users lookup, which means I had to do most of
the caching by hand (sux).

Also stripped down the user object into just the keys we are using in
the UI. This helps keep the cache small (heroku's free cache is fairly
small, and we're only using 2 fields). The cache key is also based on
the keys being fetched, so if they change, the old cache entries will no
longer be relevant and will eventually be removed.