Add initial implementation for sending notifications

apns2/client.pyi

@@ -0,0 +1,15 @@
+from typing import Optional
+
+from apns2.payload import Payload
+
+
+class APNsClient(object):
+    def __init__(self,
+                 cert_file: str,
+                 use_sandbox: bool = False,
+                 use_alternate_port: bool = False) -> None: ...
+
+    def send_notification(self,
+             token_hex: str,
+             notification: Payload,
+             topic: Optional[str] = None) -> None: ...