This commit removes support for the `id` flag from the `generate-api`
script. Additional Discovery documents are still supported via the `url`
flag.
The new behavior is to generate clients for all APIs marked as preferred
by the Discovery index if the `from_discovery` flag is `true`.
JSON has been part of the ruby stdlib since 1.9.0 (see
https://github.com/ruby/ruby/commit/af1c4167), and the latest version of
google-api-client requires ruby 2.0 or better so we can assume it's available
Daniel Azuma
Mike Moore
Google APIs
Sai Cheemalapati
Steve Bazyl
James Healy
Steven Bazyl