Supports pretty print option (w.i.p.)

With this option, GrnLine pretty-prints responses from groonga.
Now, Wrapper doesn't know it.
Wrapper: don't use response_type

"response_type" is specified in each command with "--output_type" options,
so #output_response can't detect it without parsing commands.
Wrapper: support pritty_print for JSON

TODO: support other output types (XML, TSV, MessagePack), are they needed ?
Remove needless require