Trigger a write failure if we know the connection is shutting down.
Added a send attempt limit option to ApnsConnectionConfiguration.
Merge branch 'close_connections_when_inactive' of github.com:relayrides/pushy into close_after_send_attempt_limit

Conflicts:
	src/main/java/com/relayrides/pushy/apns/ApnsConnection.java
	src/main/java/com/relayrides/pushy/apns/ApnsConnectionConfiguration.java
Added shut-down-after-send-attempt-limit functionality and tests.
Merge branch 'close_connections_when_inactive' of github.com:relayrides/pushy into close_after_send_attempt_limit
Merge branch 'close_connections_when_inactive' of github.com:relayrides/pushy into close_after_send_attempt_limit
Merge branch 'close_connections_when_inactive' of github.com:relayrides/pushy into close_after_send_attempt_limit

Conflicts:
	src/main/java/com/relayrides/pushy/apns/ApnsConnectionConfiguration.java
	src/test/java/com/relayrides/pushy/apns/ApnsConnectionTest.java
Updated copy constructor, hashCode, equals, and tests for ApnsConnectionConfiguration.
Restored some accidentally removed `final` modifiers.
Merge pull request #118 from relayrides/close_after_send_attempt_limit

Optionally close connections after a set number of send attempts