Move set_bind to before_serving hook and add close (#10)

Engine set_bind was in a before_first_request hook, and the engine was
never closed.  Moved the set_bind to a before_serving hook, and added a
pop_bind/close to an after_serving hook.

This also makes it easier to properly initialize engine in custom cli
commands.

Author: spapadim

src/gino_quart.py

@@ -97,8 +97,8 @@ async def after_response(response):
                     del request.connection
                 return response
 
-        @app.before_first_request
-        async def before_first_request():
+        @app.before_serving
+        async def before_serving():
             dsn = app.config.get("DB_DSN")
             if not dsn:
                 dsn = URL(
@@ -120,6 +120,10 @@ async def before_first_request():
                 **app.config.setdefault("DB_KWARGS", dict()),
             )
 
+        @app.after_serving
+        async def after_serving():
+            await self.pop_bind().close()
+
     async def first_or_404(self, *args, **kwargs):
         rv = await self.first(*args, **kwargs)
         if rv is None: