Derive FromValue and FromValueRef

[MarkMcCaskey]

It would be nice to be able to derive these, like Serde's Serialize and Deserialize traits. I can look into doing this, if this sounds like a good idea to you.

[murarth]

Oh, yes. This would be a good idea. I had always intended to do this, but it's slipped my mind since procedural macros were stabilized. I'll start work on this shortly. It shouldn't take long.

[murarth]

Ta-da. Just created the ketos_derive crate (and published a new version of ketos that uses it for tests). The crate doc has the list of derives supported.