treat event @fields as metrics + include/exclude metric name filters

Some filters like metrics generate events with @fields that contain only metrics
instead of trying to unrealistically specify every possible metric we make graphite output
treat @fields_are_metrics

It will also include & exclude metric names based on @include_metrics & @exclude_metrics

<pre>  graphite {
    tags               => [ "apache-metrics" ]
    fields_are_metrics => true
    include_metrics    => [ "rate_1m" ]
    host               => "localhost"
    port               => 2003
  }</pre>

The metrics are also sent in one batch instead of one by one

On carbon connection failure @reconnect_interval is now configurable
as well @resend_on_failure is configrable