Subscriptions return unsubscribe/dispose function (#527)

* Combinator return unsubscribe/dispose function

* Submittable extrinsics return UnsubFunction

* RPC methods with unsub callback returns

* Update changelog, bump version

* CHANGELOG typo

* Fix combinator unsubscribes

* Be explicit in returns for UnsubFunction (combineLatest)

packages/rpc-core/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@polkadot/rpc-core",
-  "version": "0.35.19",
+  "version": "0.36.0",
   "description": "A JavaScript wrapper for the Polkadot JsonRPC interface",
   "main": "index.js",
   "keywords": [
@@ -30,9 +30,9 @@
   "homepage": "https://github.com/polkadot-js/api/tree/master/packages/rpc-core#readme",
   "dependencies": {
     "@babel/runtime": "^7.2.0",
-    "@polkadot/jsonrpc": "^0.35.19",
-    "@polkadot/rpc-provider": "^0.35.19",
-    "@polkadot/types": "^0.35.19",
-    "@polkadot/util": "^0.33.27"
+    "@polkadot/jsonrpc": "^0.36.0",
+    "@polkadot/rpc-provider": "^0.36.0",
+    "@polkadot/types": "^0.36.0",
+    "@polkadot/util": "^0.33.28"
   }
 }