Drop deprecated metrics from 3.4, rework event counting

• Removing all deprecated metrics from 3.x release. This is a breaking change. Therefore bump to next major release.
• Add additional label terminal to all metrics of name hystrix_command_event_total.
  Use this to identify if the event is a terminal event. #19
• Marking hystrix_command_total as deprecated.
  Instead you should you should sum up all hystrix_command_event_total with state "terminal" set to "true". #19
• Marking hystrix_command_error_total as deprecated.
  Instead you should you should sum up all hystrix_command_event_total with state "terminal" set to "true"
  that you consider errors in your scenarios. #19