Add --use-v1-config option to enable new configuration format

Please refer to https://github.com/fluent/fluentd/issues/280 first.

I applied above issue result to new configuration format.
This pull request includes several refactoring to share old and new format code.

Current implemention uses `yajl` for parsing array and hash, so
the user can't add trailinig commas and can't write `#` comment.
I don't know these features are must or not.

@frsyuki @tagomoris @sonots 
Please check this pull request.