Modified: Support split of tag.

**Add config_param of split_of_tag**

An proposal. (気合)

**fluentd.conf**

```
<match app.game.*>
  type rewrite_tag_filter
  rewriterule1 server_type ^([a-z]+)$ ${tag[1]}.$1.${tag[2]}
</match>

<match game.production.api>
  type copy
  <store>
    type tdlog
    api_key hogehogehogehogehogehoge
  </store>

  <store>
    type file
    path /var/log/fluentd/production_api.log
  </store>
</match>

<match game.staging.api>
  type copy
  <store>
    type mongo
  </store>
  <store>
    type file
    path /var/log/fluentd/staging_api.log
  </store>
</match>

<match game.development.api>
  type file
  path /var/log/fluentd/development.log
</match>
```