Broken round trip for `unsigned char`

[Yankes]

This line: https://github.com/jbeder/yaml-cpp/blob/6308112e54fe41a3bc1ceeb2b807f0d09f15a1e9/include/yaml-cpp/node/convert.h#L123 load unsigned char as int But when you save you get: https://github.com/jbeder/yaml-cpp/blob/6308112e54fe41a3bc1ceeb2b807f0d09f15a1e9/include/yaml-cpp/node/convert.h#L118 Its is saved as effective char.

Or in emitter: https://github.com/jbeder/yaml-cpp/blob/master/include/yaml-cpp/emitter.h#L211