Derive macros for `elm_rs::{Elm, ElmEncode, ElmDecode, ElmQuery, ElmQueryField}`.

## Features
- `default`: None.
- `json`: Enables the derive macros for `ElmEncode` and `ElmDecode`.
- `query`: Enables the derive macro for `ElmQuery` and `ElmQueryField`.
- `serde`: Enables compatibility with serde attributes like `#[serde(rename_all = "camelCase")]`.