fix AddEmails return type and finish email tests

The GitHub docs don't make it completely clear that AddEmails is also
switching to the new v3 response format, but new integration tests
verify that it is.
add label to continue correct loop
add integration tests for user key methods

The test public key used in these tests is a key that I just generated
specifically for this purpose.  I deleted the associated private key, so
even if someone accidentally left this attached to their account, it
should have no effect.  Of course, I have no way of actually proving
that I deleted the private key, so uh... yeah.  All the more reason to
never run these integration tests using a "real" GitHub account, always
use a dedicated test account.
add link to mailing list
add line break after mailing list
first pass at tool for testing JSON fields mapping

This tool help to identify fields being returned by the GitHub API that
are not currently being mapped onto our Go data types.  Some of these
may be deliberate omissions, so these checks should only be treated as
an aid in identifying these fields, not as an absolute list of fields to
be added.
support pagination for listing gists
add Krzysztof Kowalczyk as contributor
remove Users.EditKey method

User keys can no longer be updated.  Instead, they should be deleted and
re-added.
update user integration test

add tests for User.Edit and User.GetKey
add support for repository subscription methods

(I kinda hate how long some of these names are... I'd much rather just
call them "subscriptions", but the API docs is pretty consistent about
calling them "repository subscriptions", so that's what we go with.
Maybe the intend to later add other kinds of subscriptions?)
add pagination support to Activity.ListWatchers

this is a breaking change, but there's no way around that, since the opt
param was left off initially.
renaming RepositorySubscription to Subscription

I changed my mind.  This really is terribly verbose, and looking at the
design of the API, it seems unlikely GitHub would change the
subscriptions endpoint to include anything other that repositories.  And
if they do...  well, we'll deal with it.
implement remaining Activity.Star* methods
add remaining repository methods

- Repositories.Delete
- Repositories.ListTeams
- Repositories.ListTags
- Repositories.GetBranch
start of integration tests for repo methods

Includes basic CRUD methods on repositories as well as listing branches
and tags.
add auth check to TestRepositories_CRUD
add support for listing service hooks
Add support for the milestone API
add Guz Alexander as contributor