Document the backends

The backends need to be in the documentation so that developers know
what the options are.

Change-Id: If426c95a39424232ccda2d543bdaac3844ed61a8
Partial-Bug: 1469831
Partial-Bug: 1469833

doc/source/api.rst

@@ -7,3 +7,12 @@
 
 .. automodule:: oslo_cache.exception
    :members:
+
+.. automodule:: oslo_cache.backends.memcache_pool
+   :members:
+
+.. automodule:: oslo_cache.backends.mongo
+   :members:
+
+.. automodule:: oslo_cache.backends.noop
+   :members:

oslo_cache/backends/memcache_pool.py

@@ -40,6 +40,8 @@ class ClientProxy(object):
 
 
 class PooledMemcachedBackend(memcached_backend.MemcachedBackend):
+    """Memcached backend that does connection pooling."""
+
     # Composed from GenericMemcachedBackend's and MemcacheArgs's __init__
     def __init__(self, arguments):
         super(PooledMemcachedBackend, self).__init__(arguments)

oslo_cache/backends/mongo.py

@@ -26,6 +26,10 @@ from oslo_cache import exception
 from oslo_cache._i18n import _, _LW
 
 
+__all__ = [
+    'MongoCacheBackend'
+]
+
 NO_VALUE = api.NO_VALUE
 LOG = log.getLogger(__name__)
 

oslo_cache/backends/noop.py

@@ -15,6 +15,10 @@
 from dogpile.cache import api
 
 
+__all__ = [
+    'NoopCacheBackend'
+]
+
 NO_VALUE = api.NO_VALUE