WIP: Add serde support for `Value`

[jess-sol]

Saw in #10 that full deserialization of Value to rust data types was yet to be implemented. I took an initial stab at it. I'd like to get someone more familiar with Serde to look at it, to make sure I'm on the right path. I borrowed quite a bit from the serde_json crate (specifically their Value deserializer). Deserializing the special types (like Node or Relationship) are the bits I'm not 100% sure about.

Feedback welcome, before I finish up support for V2 types. Also curious if the deserialization would be accepted standalone, or if I need to do serialization in this PR too?

TODO:

• [ ] Better error handling
• [ ] Implement V2 types
• [ ] Implement Serialization?

[0xSiO]

Thank you for looking into this! However, I've tentatively decided not to pursue this functionality for now. Value is a driver primitive that doesn't map cleanly onto serde's data types. One can fairly easily derive serde's traits on their own structs, and populate their fields using this driver (or a higher-level lib/OGM), e.g.

#[derive(Serialize, Deserialize)]
struct User {
    id: i64,
    username: String,
    email: String,
}

impl User {
    async fn find_one(id: i64) -> Result<Self, Error> {
        let node = /* run a MATCH with driver, extract User node */;
        let properties = node.properties();
        Ok(Self {
            id: node.node_identity(),
            username: properties.get("username").unwrap().clone().try_into()?,
            email: properties.get("email").unwrap().clone().try_into()?,
        })
    }
}

Something like that, anyway...

Maybe there's a compelling use case out there, though - I'm definitely willing to reconsider if that's the case.