Fix dhellmann's notes from April 18

removed the python 3 classifier. See note
e4cfa6d39d (commitcomment-6058177)

added W292 pep8 check. See note
276f7570d7 (commitcomment-6058296)

added usage examples. See note
e4cfa6d39d (commitcomment-6058130)

doc/source/usage.rst

@@ -2,6 +2,66 @@
 Usage
 ========
 
-To use  in a project::
+To use oslo.db in a project::
+
+* Session Handling
+  
+  .. code:: python
+
+    from oslo.db.sqlalchemy import session as db_session
+
+    _FACADE = None
+
+    def _create_facade_lazily():
+        global _FACADE
+        if _FACADE is None:
+            _FACADE = db_session.EngineFacade.from_config(
+                CONF.database.connection, CONF)
+        return _FACADE
+
+    def get_engine():
+        facade = _create_facade_lazily()
+        return facade.get_engine()
+
+    def get_session(**kwargs):
+        facade = _create_facade_lazily()
+        return facade.get_session(**kwargs)
+
+
+* Base class for models usage
+
+  .. code:: python
+
+	from oslo.db import models
+
+
+    class ProjectSomething(models.TimestampMixin,
+                           models.ModelBase):
+        id = Column(Integer, primary_key=True)
+        ...
+
+
+* DB API backend support 
+
+  .. code:: python
+
+    from oslo.config import cfg
+    from oslo.db import api as db_api
+
+    CONF = cfg.CONF
+    CONF.import_opt('backend', 'oslo.db.options', group='database')
+
+    _BACKEND_MAPPING = {'sqlalchemy': 'project.db.sqlalchemy.api'}
+
+    IMPL = db_api.DBAPI(CONF.database.backend, backend_mapping=_BACKEND_MAPPING)
+
+    def get_engine():
+        return IMPL.get_engine()
+
+    def get_session():
+        return IMPL.get_session()
+
+    # DB-API method
+    def do_something(somethind_id):
+        return IMPL.do_something(somethind_id)
 
-	import db