Diesel enum derive

Please note that this crate is aimed to be simple and stick to a simple usage, no fancy configuration, only Pg with Text fields.

For a more advanced usage, see this crate: adwhit/diesel-derive-enum

Usage

```rust

[derive(DieselEnum)]

pub enum Role { Admin, User, } ```

The method Role::Admin.db_value() return the database representation of this variant.