Make encryption asynchronous

We're going to need to send out a load of messages to distribute the megolm
keys; as a first step, deal with the asynchronicity this will require.

lib/crypto-algorithms/base.js

@@ -20,6 +20,7 @@ limitations under the License.
  *
  * @module crypto-algorithms/base
  */
+var q = require("q");
 
 var utils = require("../utils");
 
@@ -43,6 +44,7 @@ module.exports.DECRYPTION_CLASSES = {};
  * base type for encryption implementations
  *
  * @constructor
+ * @alias module:crypto-algorithms/base.EncryptionAlgorithm
  *
  * @param {object} params parameters
  * @param {string} params.deviceId The identifier for this device.
@@ -50,22 +52,28 @@ module.exports.DECRYPTION_CLASSES = {};
  * @param {module:OlmDevice} params.olmDevice olm.js wrapper
  * @param {string} params.roomId  The ID of the room we will be sending to
  */
-module.exports.EncryptionAlgorithm = function(params) {
+var EncryptionAlgorithm = function(params) {
     this._deviceId = params.deviceId;
     this._crypto = params.crypto;
     this._olmDevice = params.olmDevice;
     this._roomId = params.roomId;
 };
+/** */
+module.exports.EncryptionAlgorithm = EncryptionAlgorithm;
 
 /**
- * Initialise this EncryptionAlgorithm instance for a particular room
+ * Initialise this EncryptionAlgorithm instance for a particular room.
  *
- * @method module:crypto-algorithms/base.EncryptionAlgorithm#initRoomEncryption
- * @abstract
+ * <p>This will be called once per EncryptionAlgorithm, just after the
+ * constructor is called.
  *
  * @param {string[]} roomMembers list of currently-joined users in the room
  * @return {module:client.Promise} Promise which resolves when setup is complete
  */
+EncryptionAlgorithm.prototype.initRoomEncryption = function(roomMembers) {
+    return q();
+};
+
 
 /**
  * Encrypt a message event
@@ -77,7 +85,7 @@ module.exports.EncryptionAlgorithm = function(params) {
  * @param {string} eventType
  * @param {object} plaintext event content
  *
- * @return {object} new event body
+ * @return {module:client.Promise} Promise which resolves to the new event body
  */