update some file names

default config file is now `jupyterhub_config.py`,
to be consistent with everything else

add config files, runtime files to .gitignore

examples/postgres/hub/jupyterhub_config.py

@@ -0,0 +1,17 @@
+# Configuration file for jupyterhub (postgres example).
+
+c = get_config()
+
+# Add some users.
+c.JupyterHubApp.admin_users = {'rhea'}
+c.Authenticator.whitelist = {'ganymede', 'io', 'rhea'}
+
+# These environment variables are automatically supplied by the linked postgres
+# container.
+import os;
+pg_pass = os.getenv('POSTGRES_ENV_JPY_PSQL_PASSWORD')
+pg_host = os.getenv('POSTGRES_PORT_5432_TCP_ADDR')
+c.JupyterHubApp.db_url = 'postgresql://jupyterhub:{}@{}:5432/jupyterhub'.format(
+    pg_pass,
+    pg_host,
+)