Fixes #371.

Change-Id: I97f2fc28ce048442ee8af3bd11c48b5b2084e09b

Note that this is an API-breaking change but should have minimal
impact on users of this package due to the nice inference
properties of the Go programming language.

Bumped `libraryVersion` to `2` due to API-breaking change as
discussed in #376.

Fixes #180.

Change-Id: Ib386135e6b8f306d1f54278968c576f3ceccc4e7

Additionally, change preview media type to documented custom media type
for https://developer.github.com/v3/orgs/teams/#check-if-a-team-manages-a-repository

Fixes #262.

Change-Id: Ie9acf859346fce6b797b039d35b17e46f404e2a3

- Add new options struct to AddCollaborator (BREAKING CHANGE)
- Add Permissions field to User struct, which gets populated when
  calling ListCollaborators

This includes all of the methods mentioned in this blog post:
https://developer.github.com/changes/2014-03-18-paginating-method-changes/
as well as a handful of others I found.  Sadly, this is a breaking
change for many of these methods because it changes the method
signature, but with yesterday's API change these methods are now broken
anyway. :(

this change also includes some additional minor code cleanup

fixes #58