Implement receipt handling and expose new Room functions

Add polyfills for Array.map/filter according to MDN because it looks much
better than the utils format.

Add stub tests for edge cases and implement test for the common case.

index.js

@@ -1,3 +1,6 @@
 var matrixcs = require("./lib/matrix");
 matrixcs.request(require("request"));
 module.exports = matrixcs;
+
+var utils = require("./lib/utils");
+utils.runPolyfills();