v0.4.0 retrieve ALL tweets since (fixes #10)

before version 0.4.0, when fetching more than 200 tweets,
grailbird_updater would ignore that with only one request you can only
fetch 200 tweets at a time from the API. 0.4.0 fixes that as well as
adding the method make_twitter_request and removing the limit option
which was kind of pointless in the first place.