Using both user name and email for gh-pages commits.

The Travis logs indicate git is hinting that both an
email and a name should be set:

> Update docs after merge to master.
>  Committer: selfiebot <travis@testing-worker-linux-docker-981a76b7-3328-linux-4.prod.travis-ci.org>
> Your name and email address were configured automatically based
> on your username and hostname. Please check that they are accurate.
> You can suppress this message by setting them explicitly:
>     git config --global user.name "Your Name"
>     git config --global user.email you@example.com
> After doing this, you may fix the identity used for this commit with:
>     git commit --amend --reset-author

From https://travis-ci.org/GoogleCloudPlatform/gcloud-python/builds/44498713
Merge pull request #442 from dhermes/fix-user-and-email

Using both user name and email for gh-pages commits.
Adding a non-protobuf allocate_ids method on Dataset.

Partially address #336.
Removing xrange and making test _Key return _Key instances.