Add documentation about request.app

docs/sanic/request_data.md

@@ -69,6 +69,23 @@ The following variables are accessible as properties on `Request` objects:
   
 - `ip` (str) - IP address of the requester.
 
+- `app` - a reference to the Sanic application object that is handling this request. This is useful when inside blueprints or other handlers in modules that do not have access to the global `app` object.
+
+```python
+from sanic.response import json
+from sanic import Blueprint
+
+bp = Blueprint('my_blueprint')
+
+@bp.route('/')
+async def bp_root(request):
+    if request.app.config['DEBUG']:
+        return json({'status': 'debug'})
+    else:
+        return json({'status': 'production'})
+
+```
+
 ## Accessing values using `get` and `getlist`
 
 The request properties which return a dictionary actually return a subclass of