update docs for 0.4.0

Author: jreback

docs/source/whatsnew.rst

@@ -18,6 +18,7 @@ What's New
 
 These are new features and improvements of note in each release.
 
+.. include:: whatsnew/v0.4.0.txt
 .. include:: whatsnew/v0.3.0.txt
 .. include:: whatsnew/v0.2.1.txt
 .. include:: whatsnew/v0.2.0.txt

docs/source/whatsnew/v0.4.0.txt

@@ -1,9 +1,9 @@
 .. _whatsnew_040:
 
-v0.4.0 (???)
--------------------------
+v0.4.0 (May 15, 2017)
+---------------------
 
-This is a major release from 0.3.0 and includes new features and a number of bug fixes.
+This is a major release from 0.3.0 and includes compat with pandas 0.20.1, and some backwards incompatible API changes.
 
 Highlights include:
 
@@ -13,20 +13,16 @@ Highlights include:
 
 .. _whatsnew_040.enhancements:
 
-New features
+Enhancements
 ~~~~~~~~~~~~
 
-Other enhancements
-^^^^^^^^^^^^^^^^^^
-
-.. _whatsnew_040.bug_fixes:
-
-Bug Fixes
-~~~~~~~~~
+- Compat with pandas 0.20.1 (:issue:`304`, :issue:`320`)
+- Switched test framework to use ``pytest`` (:issue:`310`, :issue:`312`)
 
 .. _whatsnew_040.api_breaking:
 
 Backwards incompatible API changes
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
 - Support has been dropped for Python 2.6 and 3.4 (:issue:`313`)
 - Support has been dropped for `pandas` versions before 0.17.0 (:issue:`313`)