Migrate to libyaml-safer

[acatton]

My goal is to get rid of unsafe {} blocks. I think the Rust community is too aggressive with unsafe {}. I know that it's impossible to avoid when working with C library.

However, I love the initiative from @simonask "libyaml-safer".

I'm hoping to find time to start migrating to it, and clean up all the unsafe blocks in serde-yaml-ng. I'm happy to fix stuff on libyaml-safer if necessary. (this is why I'm pinging Simon on this issue :) )

[simonask]

Let me know if you have any questions or if there is anything I can do to help out. :-)

[acatton]

Absolutely, thank you for your work Simon 👍