cleanup of hacking.rst heat doc

removed unneccessary capitalizations
Heat should be lower case
titles should be lower case as well
changed document to documents and features
https://wiki.openstack.org/wiki/Documentation/Conventions

Change-Id: I55a4c93f518834b5d508f6ef5237ee202df37560

HACKING.rst

@@ -1,19 +1,19 @@
-Heat Style Commandments
+Heat style commandments
 =======================
 
-- Step 1: Read the OpenStack Style Commandments
+- Step 1: Read the OpenStack style commandments
   http://docs.openstack.org/developer/hacking/
 - Step 2: Read on
 
-Heat Specific Commandments
+Heat specific commandments
 --------------------------
 
 None so far
 
-Creating Unit Tests
+Creating unit tests
 -------------------
 For every new feature, unit tests should be created that both test and
-(implicitly) document the usage of said feature. If submitting a patch for a
+(implicitly) document the usage of said features. If submitting a patch for a
 bug that had no unit test, a new passing unit test should be added. If a
 submitted bug fix does have a unit test, be sure to add a new one that fails
 without the patch and passes with the patch.
@@ -22,7 +22,7 @@ For more information on creating unit tests and utilizing the testing
 infrastructure in OpenStack Heat, please read heat/tests/testing-overview.txt.
 
 
-Running Tests
+Running tests
 -------------
 The testing system is based on a combination of tox and testr. The canonical
 approach to running tests is to simply run the command `tox`. This will