Add file_type 'hash'

Current file types require us to convert logs as csv, tsv, json strings
previous enqueue fluentd. But fluent plugins can get Hash object directlly
through msgpack. Especially in ruby, a cost to convert JSON is higher than msgpack
converting.

This commit add file type 'hash' to receive Hash log format.
Rename methods to be more "colorful"
Add top layer on msgpack data record
Rename new file_type to msgpack from hash
Merge branch 'adorechic-hash_type'