Support table generation

[n3wscott]

This is a work in progress to produce a supported features table from yaml config via a cli.

The work to be done is to add more support for URLs to link back to specs and features at versions. See cloudevents/spec#1048 for the history.

---

The config template looks like this:

(╯°□°)╯︵  go run ./cmd/features template LANG
language: LANG
versions:
  v1.0:
    core: false
    formats:
      avro: false
      amqp: false
      json: false
      protobuf: false
    bindings:
      amqp:
        binary: false
        structured: false
      http:
        binary: false
        structured: false
        batch: false
      kafka:
        binary: false
        structured: false
      mqtt:
        binary: false
        structured: false
      nats:
        binary: false
        structured: false
      web-sockets:
        binary: false
        structured: false

And the table is rendered as such:

(╯°□°)╯︵  go run ./cmd/features render ./cmd/features/testdata/foo.yaml ./cmd/features/testdata/bar.yaml ./cmd/features/testdata/baz.yaml

Feature		Foo	Bar	Baz
v1.0
CloudEvents Core		✔️	✔️	❌
Avro Event Format		✔️	✔️	❌
AMQP Event Format		✔️	✔️	❌
JSON Event Format		✔️	✔️	❌
Protobuf Event Format		✔️	✔️	❌
AMQP	Binary	✔️	✔️	❌
	Structured	✔️	✔️	❌
HTTP	Binary	✔️	✔️	❌
	Structured	✔️	✔️	❌
	Batch	✔️	✔️	❌
Kafka	Binary	✔️	✔️	❌
	Structured	✔️	✔️	❌
MQTT	Binary	✔️	✔️	❌
	Structured	✔️	✔️	❌
NATS	Binary	✔️	✔️	❌
	Structured	✔️	✔️	❌
Web Sockets	Binary	✔️	✔️	❌
	Structured	✔️	✔️	❌
v0.3
CloudEvents Core		✔️	❌	❌
Avro Event Format		✔️	❌	❌
AMQP Event Format		✔️	❌	❌
JSON Event Format		✔️	❌	❌
Protobuf Event Format		✔️	❌	❌
AMQP	Binary	✔️	❌	❌
	Structured	✔️	❌	❌
HTTP	Binary	✔️	❌	❌
	Structured	✔️	❌	❌
	Batch	✔️	❌	❌
Kafka	Binary	✔️	❌	❌
	Structured	✔️	❌	❌
MQTT	Binary	✔️	❌	❌
	Structured	✔️	❌	❌
NATS	Binary	✔️	❌	❌
	Structured	✔️	❌	❌
Web Sockets	Binary	✔️	❌	❌
	Structured	✔️	❌	❌

[n3wscott]

I am hoping someone can fork this and continue the work if there is interest. Thanks!