Support <record></record> directive

This is coming brand new config format like [fluent-plugin-record-reformer](https://github.com/sonots/fluent-plugin-record-reformer).

The configuration sample is below.

```
# Current
<match input.access>
  type                 geoip
  geoip_lookup_key     host
  enable_key_latitude  geoip_lat
  enable_key_longitude geoip_lon
  enable_key_lonlat    geoip_lonlat
  remove_tag_prefix    input.
  add_tag_prefix       geoip.
</match>

# Brand new config format
<match input.access>
  type                 geoip
  geoip_lookup_key     host
  <record>
    geoip_lat          ${latitude['host']}
    geoip_lon          ${longitude['host']}
    geoip_lonlat       [${longitude['host']},${latitude['host']}]
  </record>
  remove_tag_prefix    input.
  add_tag_prefix       geoip.
</match>
```

c.f. https://github.com/y-ken/fluent-plugin-geoip/pull/7#issuecomment-38537347