Updated CHANGES and UPGRADE to reflect registration API changes.

CHANGES.rst

+Latest
+======
+
+Registration API:
+ * The registration API has been overhauled to function like the login API. In
+   practice, this means registration requests must now include the following:
+   'type':'m.login.password'. See UPGRADE for more information on this.
+ * The 'user_id' key has been renamed to 'user' to better match the login API.
+ * There is an additional login type: 'm.login.email.identity'.
+ * The command client and web client have been updated to reflect these changes.
+
 Changes in synapse 0.2.3 (2014-09-12)
 =====================================
 

UPGRADE.rst

+Upgrading to Latest
+===================
+
+This registration API now closely matches the login API. This introduces a bit
+more backwards and forwards between the HS and the client, but this improves
+the overall flexibility of the API. You can now GET on /register to retrieve a list
+of valid registration flows. Upon choosing one, they are submitted in the same
+way as login, e.g::
+
+  {
+    type: m.login.password,
+    user: foo,
+    password: bar
+  }
+
+The default HS supports 2 flows, with and without Identity Server email
+authentication. Enabling captcha on the HS will add in an extra step to all
+flows: ``m.login.recaptcha`` which must be completed before you can transition
+to the next stage. There is a new login type: ``m.login.email.identity`` which
+contains the ``threepidCreds`` key which were previously sent in the original
+register request. For more information on this, see the specification.
+
+
 Upgrading to v0.2.0
 ===================