Parse IP addresses, MAC addresses, and email addresses

add support for pointers and TextUnmarshaler

Add support for time.Duration fields

Add support for environment variables

Resolve some merge conflicts from #8

As with the previous key added in 19c0916, I deleted the associated
private key using /usr/bin/shred.  But of course, I have no way to prove
that.  Again, all the more reason to always use a test account when
running these integration tests.

see 92bbb1ce51

This adds support and integration tests for editing branch protection.

MustParse returns *Parser

For more information about the preview see here:
https://developer.github.com/changes/2015-11-11-protected-branches-api/

This adds only retrieving the information and not setting it. Setting
will come in a later commit (if that one here is okay).

I tried to follow the naming guidelines as much as possible and
hopefully I made it right the first time. :-)

Adding the new BasicAuthTransport raises the minimum required version of
go to 1.4.

Add a new error type, TwoFactorAuthError, which identifies the need to
include a one-time password when using Basic Auth for a user with
two-factor auth enabled.

An example of using both the new transport and error type can be seen in
examples/basicauth/main.go.

fixes #258

[docs] Tidy up README formatting.

Both:
https://developer.github.com/v3/issues/#list-issues
https://developer.github.com/v3/issues/#list-issues-for-a-repository

State that the default is `desc` for direction. (As does my results). So
update the comment.

In particular, this handles the case of trying to decode No Content
(204) responses.

[feature] NotFoundHandler on Subrouters is now called correctly.

Previously, concurrent calls to Client.Do would have data races writing
Client.Rate. Protect it with a mutex.

Resolves #253.

This test focuses on the feature of allowing sub-routers error handlers to precede the parents, rather than the code change required to provide this functionality.