Update CHANGELOG.txt for 8.x-3.0-alpha4.

CHANGELOG.txt

@@ -1,13 +1,17 @@
-8.x-3.0, 2015-12-04
--------------------
+8.x-3.x-dev
+-----------
 
 This is the first full Drupal 8 port.
 
  - The procedural API is gone. The hook is replaced by an annotated plugin type,
    and the custom tag table with a config entity type.
  - Custom tags use Twig templates instead of HTML and PHP code.
  - Removed all special tag properties (nocode, plain, selfclosing).
-
+ - Rewrote the parsing algorithm, and used the prepare() phase of the
+   filter. Tags are now validated before any other filters are applied, and
+   attributes as well as tag.source bypass all text filtering.
+   Tag content is now rendered on demand only if the tag's renderer uses it.
+ - The module now contains unit tests.
 
 2012-02-19