Migrate to v11

- https://gist.github.com/frsyuki/6191818
 - 1. use module Fluentd; module Plugin namespace
 - 2. use collector.emit
 - 3. use fluentd-plugin-XXX gem package
- disuse JSON parse config_param value
- disuse Fluent::Engine.now

But not running yet. Require v11 ConfigPlaceholders.