v0.13.0 - Improvements everywhere!

This release contains a wide assortment of improvements to Pushy.

• Added an entirely separate benchmark server to make sure that our benchmarks are measuring client performance and not secretly measuring the performance of the server instead (#585)
• Added support for the apns-id header (#577)
• We no longer treat InternalServerError responses from the APNs server as write exceptions, and instead treat them as rejections (#576)
• Changed the default expiration time for push notifications from "immediate" to 24 hours (#593)
• Spread connections across all available APNs servers by using round-robin DNS resolution (#594)
• Added a separate metrics listener using the Micrometer application monitoring facade (#597)
• Perform protocol negotiation directly and drop ALPN entirely (#598)
• Dropped Apache Commons Codec as a dependency (#599)
• Improved exception handling and reporting when something goes wrong while opening a new connection (#602)
• Updated to Netty 4.1.23 (#596)

Please note that because we no longer use ALPN for protocol negotiation, use of alpn-agent or a native SSL provider is no longer required, but users can still expect significant performance gains from a native SSL provider.

For a complete list of changes in this release, please see the v0.13.0 milestone.