* Update Serving Rest API example
This change updates the sample to use a Knative Service instead of a
Route and Configuration directly.
It also updates the instructions to:
* Add links to relevant external documentation
* Clarify steps and actions occuring in each step
* Use label selectors for querying child resources
* Require Knative 0.3 to simplify instructions
* Add missing backticks
* Updating numbering to use 1.
* Update docs to use correct ingress gateway service.
* Update wording of knative-ingressgateway deprecation.
* Update wording of knative-ingressgateway deprecation per feeeback.
* Update docs to use kubectl long flags
* adding back in the --filename flag (lost when manually merged)
* notice a few missed
* notice a few missed '-f' flags
* change -o to --output
* Rename samples to languge-specific folders
* Remove steren-app and steren-function since they aren't working
* Rename buildpack folders
* Rename buildpack-function