feat: add engine.start() and engine.stop() API

Author: sdjcw

Pipfile

@@ -21,6 +21,7 @@ six = ">=1.11.0"
 qiniu = "<=7.1.4"
 requests = ">=2.12.1"
 werkzeug = "*"
+gevent = ">=1.0.2,<2.0.0"
 typing = { version = "*", markers = "python_version < '3.5.0'" }
 pyopenssl = { version = "*", markers = "python_version < '2.7.9'" }
 idna = { version = "*", markers = "python_version < '2.7.9'" }