New Features:
- #797 Support ServiceAccountCredential in netstandard, without X509 certificates...
- #807 ...and add X509 certificate support.
Bug fixes:
- #79 Get the generated discovery to discover its own discovery document.
- #812 Fix xmldoc formatting in generated code for resumable methods.
- #813 Fix PromptCodeReceiver on .NET Core.
- #815 Add missing Google.Apis dependency in .NET45
- #816 Strongly name netstandard generated libraries.
Testing: