4.2.0 - Container Identifiers

What's Changed

Container Identifiers by @dimitribouniol in #58

To help users who need to configure a production and development container, added two new containerIDs: production and development. Also added documentation and clarified how the default ID is used, which isn’t always the default depending on how use is called.

Note: Since this is new, I went with development instead of sandbox here because all of Apple’s documentation refers to it as the development environment. We should probably add .development and deprecate .sandbox in APNSwift as well.

This patch was released by @0xTim

Full Changelog: 4.1.0...4.2.0