Add support for rustCustomDerive and rustCustomUse metadata

[AdamLeyshon]

This allows us to additional use statements or derive macros on generated structs as per my request in #30

rustCustomUse is a string of use statments separated by ;
It supports single and multi-import statements.
For example: serde::{Deserialize, Serialize} or serde::Serialize are both valid.

rustCustomDerive is a string of derive identifers separated by ,
For example: FromSqlRow,AsExpression,Debug,Default

JTD JSON Example:

{
  "metadata": {
    "rustCustomDerive": "FromSqlRow, AsExpression, Debug, Default",
    "rustCustomUse": "std::fmt::Debug;crate::lib::crypto::{hash_string, sign_string}"
  },
  "properties": {
    "inventory": {
      "metadata": {
        "rustCustomDerive": "Default,Debug"
      },
      "properties": {
        "threshold": {
          "type": "uint32"
        }
      }
    }
  }
}

Outputs the following:

// Code generated by jtd-codegen for Rust v0.2.1

use crate::lib::crypto::{hash_string, sign_string};
use serde::{Deserialize, Serialize};
use std::fmt::Debug;

#[derive(Serialize, Deserialize, Default, Debug)]
pub struct ApiConfigDataInventory {
    #[serde(rename = "threshold")]
    pub threshold: u32,
}

#[derive(Serialize, Deserialize, FromSqlRow,  AsExpression,  Debug,  Default)]
pub struct ApiConfigData {
    #[serde(rename = "inventory")]
    pub inventory: ApiConfigDataInventory,
}

[ucarion]

Hi, I just want to acknowledge that I've seen this PR, and that I'll try to get to it when time permits.

Thanks so much for taking the time to contribute!

[frenzox]

Any chance this gets merged?

[AdamLeyshon]

@frenzox I raised this PR almost exactly a year ago, looks like the whole JTD org/projects are dead, there's been no activity in any of the repos for months except for Dependabot PRs.

[alissapajer]

This is exactly what we need! Merging this in to my fork. Thank you!

[alissapajer]

Rust custom derives for all generated types: https://github.com/spindle-app/json-typedef-codegen/pull/4/files