Add pubsub interface definition (#54)

* Add pubsub interface definition

* Functional JsonRpcCoder

* Functional HttpProvider

* Functional WsProvider

* Functional split completed

* Split actual method subscription

* Update flow

* Flatten no user-specified array in sub call

packages/api-provider/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@polkadot/api-provider",
-  "version": "0.7.1",
+  "version": "0.8.0",
   "description": "Transport providers for the API",
   "main": "index.js",
   "keywords": [
@@ -34,7 +34,7 @@
     "nock": "^9.1.0"
   },
   "dependencies": {
-    "@polkadot/util": "^0.13.1",
+    "@polkadot/util": "^0.17.2",
     "babel-runtime": "^6.26.0",
     "isomorphic-fetch": "^2.2.1",
     "websocket": "^1.0.25"