Add type annotations (PEP 484) (#25)

apns2/errors.py

@@ -1,3 +1,6 @@
+from typing import Type, Optional
+
+
 class APNsException(Exception):
     pass
 
@@ -128,7 +131,7 @@ class MethodNotAllowed(InternalException):
 class Unregistered(APNsException):
     """The device token is inactive for the specified topic."""
 
-    def __init__(self, timestamp=None):
+    def __init__(self, timestamp: Optional[str] = None) -> None:
         super(Unregistered, self).__init__()
 
         self.timestamp = timestamp
@@ -164,7 +167,7 @@ class Shutdown(APNsException):
     pass
 
 
-def exception_class_for_reason(reason):
+def exception_class_for_reason(reason: str) -> Type[APNsException]:
     return {
         'BadCollapseId': BadCollapseId,
         'BadDeviceToken': BadDeviceToken,