* Issue #5147: allow empty values for properties.
* Issue #5147: Allow multiple `-D` options.
* Issue #5147: take advantage (and demonstrate) the new usage of -D.
* Issue #5147: also update windows script and security ones.
* Another approach: extending NodeJS server to support GCF.
This does not add a new language, but adding some client options
to support Google Cloud Functions (GCF).
* Add URLs for how to deploy the generated code.
Adds the client options help message and the README.md file.