serde_yaml instead of yaml-rust

[alexanderjanke]

Hi,

I've noticed simetry uses serde and serde_json, and also yaml-rust. yaml-rust doesn't seem to have serde's traits implemented. Maybe it would be better to use a library like serde_yaml for Serde support. This is a breaking change, but it would unify the usage for YAML and JSON. My use case would be to use from_value to convert the iRacing Yaml to a typed struct.

Also, yaml-rust doesn't seem to be maintained.