Add some Action Cable CHANGELOG entries

And improve changelongs.

[ci skip]

actioncable/CHANGELOG.md

 ## Rails 5.0.0.beta2 (February 01, 2016) ##
 
-*   No changes.
+*   Support PostgreSQL pubsub adapter.
 
+    *Jon Moss*
+
+*   Remove EventMachine dependency.
+
+    *Matthew Draper*
+
+*   Remove Celluloid dependency.
+
+    *Mike Perham*
 
 *   Create notion of an `ActionCable::SubscriptionAdapter`.
     Separate out Redis functionality into

actionpack/CHANGELOG.md

 ## Rails 5.0.0.beta2 (February 01, 2016) ##
 
-*   No changes.
-
-
 *   Add `-g` and `-c` (short for _grep_ and _controller_ respectively) options
     to `bin/rake routes`. These options return the url `name`, `verb` and
     `path` field that match the pattern or match a specific controller.

actionview/CHANGELOG.md

 ## Rails 5.0.0.beta2 (February 01, 2016) ##
 
-*   No changes.
-
-
 *   Fix stripping the digest from the automatically generated img tag alt
     attribute when assets are handled by Sprockets >=3.0.
 

activerecord/CHANGELOG.md

 ## Rails 5.0.0.beta2 (February 01, 2016) ##
 
-*   No changes.
-
-
 *   `ActiveRecord::Relation#reverse_order` throws `ActiveRecord::IrreversibleOrderError`
     when the order can not be reversed using current trivial algorithm.
     Also raises the same error when `#reverse_order` is called on

activesupport/CHANGELOG.md

 ## Rails 5.0.0.beta2 (February 01, 2016) ##
 
-*   No changes.
-
-
 *   Change number_to_currency behavior for checking negativity.
 
     Used `to_f.negative` instead of using `to_f.phase` for checking negativity

railties/CHANGELOG.md

 ## Rails 5.0.0.beta2 (February 01, 2016) ##
 
-*   No changes.
-
-
 *   Add `after_bundle` callbacks in Rails plugin templates.  Useful for allowing
     templates to perform actions that are dependent upon `bundle install`.
 
@@ -26,6 +23,7 @@
 
     *Will Fisher*
 
+
 ## Rails 5.0.0.beta1 (December 18, 2015) ##
 
 *   Newly generated plugins get a `README.md` in Markdown.