deleteAlias() support

lib/client.js

@@ -1458,6 +1458,22 @@ MatrixClient.prototype.createAlias = function(alias, roomId, callback) {
     );
 };
 
+/**
+ * Delete an alias to room ID mapping.  This alias must be on your local server (I hope).
+ * @param {string} alias The room alias to delete.
+ * @param {module:client.callback} callback Optional.
+ * @return {module:client.Promise} Resolves: TODO.
+ * @return {module:http-api.MatrixError} Rejects: with an error response.
+ */
+MatrixClient.prototype.deleteAlias = function(alias, roomId, callback) {
+    var path = utils.encodeUri("/directory/room/$alias", {
+        $alias: alias
+    });
+    return this._http.authedRequest(
+        callback, "DELETE", path, undefined, undefined
+    );
+};
+
 /**
  * Get room info for the given alias.
  * @param {string} alias The room alias to resolve.