Includes additions to User, Organization, Repository, and Gist.  Some
minor changes to existing fields based on changes in the v3 API (for
example, Gist.User became Gist.Owner).  Most everything else is new
additions.

refs #103

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. :(

it's not the cleanest, but it works.

instead of inspecting the JSON tags on the struct fields directly,
actually run it through JSON marshalling and unmarshalling, then compare
those results.

So it appears GitHub already supports multiple types of subscriptions:
repositories and threads.  I'm leaving the data type simply as
'Subscription', but am updating the method names to avoid confusion,
since they're both part of the ActivitiesService.

mark RateLimit method as deprecated in favor of RateLimits which returns
both the core and search limits. (see deprecation notice in API docs:
https://developer.github.com/v3/rate_limit/#deprecation-notice)

Includes basic CRUD methods on repositories as well as listing branches
and tags.

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.

(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 tests for User.Edit and User.GetKey

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.

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.

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.

This is a breaking change, but it appears that this method has been
broken for some time now and no one has complained yet, so I'm going to
assume no one is using it yet.

Notably, this is also the first (of many, I'm sure) bug I've discovered
while working on the new integration tests (#98).  Yay for better tests!