<<< Breaking change >>>
In the functions unpack() and parse(),
Old behavior: If any parse error is happend, offset is NOT updated.
New behavior: If any parse error is happend, offset is updated to the
position the error happened.
It helps MessagePack format error analysis.
If you want to old behavior, copy the original value of offset and then call unpack()
and/or parse().
Renamed names that related to a visitor.
Renamed test name from json to json_like because I omit escape.
Added end_map_value() and end_map() implementation.
