Add uploadContent method

lib/client.js

@@ -462,6 +462,16 @@ MatrixClient.prototype.sendHtmlMessage = function(roomId, body, htmlBody, callba
     return this.sendMessage(roomId, content, callback);
 };
 
+/**
+ * @param {File} file object
+ * @param {module:client.callback} callback Optional.
+ * @return {module:client.Promise} Resolves: TODO
+ * @return {module:http-api.MatrixError} Rejects: with an error response.
+ */
+MatrixClient.prototype.uploadContent = function(file, callback) {
+    return this._http.uploadContent(file, callback);
+};
+
 /**
  * @param {string} roomId
  * @param {boolean} isTyping