Write ErrorResponse class

When notifications cannot be delivered or other errors occur, the connection
sends back some data to help identify the problem. The ErrorResponse class
decodes the data and gives us access to the status and identifier of the
notification related to the error.
fixup error_response
jruby requires jruby-openssl
Close connection at error.

Conflicts:
	lib/grocer/connection.rb
	lib/grocer/notification.rb
	lib/grocer/pusher.rb
call destroy/disconnect in all places close
add delegates
don't throw away the ssl object, just disconnect
add push_batch and non-blocking read errors
fix InvalidCommandError and more clear can_read? code (thnx stevenharman)