DOC : added folders for api_changes and whats_new

Added README + folders for whats_new and api_changes files.

The idea is instead of everyone editing the same file (which leads to
frequent conflicts requiring either manual merging or re-basing) each
entry will create a new file which will be assembled into a single file
during the release.

Author: tacaswell

doc/api/api_changes/README.txt

@@ -0,0 +1,9 @@
+For changes which require an entry in `api_changes.rst` please create a file
+in this folder with the name YYYY-MM-DD-[initials].rst (ex 2014-07-31-TAC.rst)
+with contents following the form:
+
+Brief destription of change
+```````````````````````````
+
+Long description of change, justification, and work-arounds to
+maintain old behavior (if any).

doc/users/whats_new/README.txt

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+This folder is for placing new portions of `whats_new.rst`.
+
+When adding an entry please look at the currently existing files to see
+if you can extend any of them.  If you create a name name it `cool_new_feature.rst`
+and include contentents of the form:
+
+Section Title for Feature
+-------------------------
+
+A bunch of text about how awesome the new feature is and examples of how
+to use it.
+
+A sub-section
+`````````````