add pagination support, for getting forks

Adds a forksForPage that allows the user to contol which pages are
requested.

githubGetPage requests the maximum allowed 100 results per page, to
minimize the API calls needed.
Merge remote-tracking branch 'upstream/master'
add starring interface

Since these are new functions, I made them all take a Maybe GithubAuth.

Only implemented the parts I need, which does not include the api to
star and unstar a repository, or check if a single repository is starred
by the authed user.
Merge branch 'master' of git://github.com/joeyh/github