Update README.md to include recently-added APIs.
Update README.md to include recently-added APIs.

Update code samples for storage and datastore to use newer API.

Change-Id: I1eb764a3a93c4b3f6d3dc5386d95a841552dab87
Reviewed-on: https://code-review.googlesource.com/3944
Reviewed-by: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@google.com>

michael-grosshans/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,michael-grosshans/google-cloud-go