Pushjack

-------------------

- apns: Remove TLS version flag and default to ``ssl.PROTOCOL_TLS`` when creating APNS socket connection. Thanks `Tanner Stirrat`_!

-------------------

- gcm: Use FCM URL instead of deprecated GCM URL. Thanks `Lukas Anzinger`_!

-------------------

- apns: Remove restriction on token length due to incorrect assumption about tokens always being 64 characters long.

-------------------

- apns: Add exceptions ``APNSProtocolError`` and ``APNSTimeoutError``. Thanks `Jakub Kleň`_!
- apns: Add retry mechanism to ``APNSClient.send``. Thanks `Jakub Kleň`_!

- Add ``default_retries`` argument to ``APNSClient`` initialization. Defaults to ``5``.
- Add ``retries`` argument to ``APNSClient.send``. By default will use ``APNSClient.default_retries`` unless explicitly passed in.
- If unable to send after ``retries``, an ``APNSTimeoutError`` will be raised.

- apns: Fix bug in bulk ``APNSClient.send`` that resulted in an off-by-one error for message identifier in returned errors. Thanks `Jakub Kleň`_!
- apns: Add max payload truncation option to ``APNSClient.send``. Thanks `Jakub Kleň`_!

- Add ``default_max_payload_length`` argument to ``APNSClient`` initialization. Defaults to ``0`` which disabled max payload length check.
- Add ``max_payload_length`` argument to ``APNSClient.send``. By default will use ``APNSClient.default_max_payload_length`` unless explicitly passed in.
- When ``max_payload_length`` set, messages will be truncated to fit within the length restriction by trimming the "message" text and appending it with "...".

-------------------

- apns: Optimize reading from APNS Feedback so that the number of bytes read are based on header and token lengths.
- apns: Explicitly close connection to APNS Feedback service after reading data.
- apns: Add support for ``mutable-content`` field (Apple Notification Service Extension) via ``mutable_content`` argument to ``APNSClient.send()``. Thanks `Ahmed Khedr`_!
- apns: Add support for ``thread-id`` field (group identifier in Notification Center) via ``thread_id`` argument to ``APNSClient.send()``. Thanks `Ahmed Khedr`_!

-------------------

- apns: Fix implementation of empty APNS notifications and allow notifications with ``{"aps": {}}`` to be sent. Thanks `Julius Seporaitis`_!