Add Namespace info

[JeremyParish69]

With the recent launch of ICNS, namespace is on mind.

We could have an object property just for namespaces?

...
"namespaces": {
  "icns": true,
  "starname": false,
  "stargaze's namespace": false
},
...

Or each namespace could be an allowed keyword within 'features'?

...
"features": [
  "suggest-chain",
  "icns",
  "starname-namespace"
],
...

[pyramation]

let's keep it in features, seems good to me.