Serde_yaml deprecated

[bdarcus]

Will have to see what alternative emerges from the decision.

https://github.com/dtolnay/serde-yaml/releases/tag/0.9.34

EDIT:

https://github.com/saphyr-rs/saphyr (this is a ground up rewrite of YAML in Rust, with intention to add serde support in a separate repo)
https://github.com/sebastienrousseau/serde_yml (doesn't seem very viable)