customdebugderive

Derive Debug with a custom format per field.

Usage

```rust #[macrouse] extern crate customdebug_derive; use std::fmt;

#[derive(CustomDebug)]
struct Foo {
    #[debug(format = "{} things")]
    n: i32,
    #[debug(with = "hex_fmt")]
    m: i32,
}

fn hex_fmt<T: fmt::Debug>(n: &T, f: &mut fmt::Formatter) -> fmt::Result {
    write!(f, "0x{:02X?}", n)
}

```

Would print something like

Foo { n: 42 things, m: 0xAB }