API broken

[unknwon]

Hi, looks like oatuh2.Flow(https://github.com/martini-contrib/oauth2/blob/master/oauth2.go#L169) no longer exists in golang/oauth2 ?

[jnfeinstein]

+1 to merge, code looks fine to me. This is blocking builds. :(

[weslleyandrade]

Again broke API.
I made a new pull request to fix. #45