fetch access token
fetch access token

Some initial code to fetch the access token and secret from Twitter by
asking the user to visit a URL in their browser, authorize the application
and then enter the generated PIN.

This should be cleaned up a bit, and then it should be possible for users
to add new profiles with:

    twarc configure <profile>

Which would reuse the consumer key and consumer secret on the main profile
and ask them to repeat the process.

refs #177

edsu/twarc,hugovk/twarc,remagio/twarc,remagio/twarc,DocNow/twarc