No way to emit `YAML::Binary` in literal, single-quoted or plain form.

[sxrzh]

As mentioned in issue #1287 , YAML::Literal does not work for YAML::Binary.
In fact, YAML::SingleQuoted does not work for YAML::Binary either. Besides there is no way to emit YAML::Binary without quotes. Currently the emitter applies double-quoted style for all binary nodes.