Support thiserror like formatting for Display derive

[Luro02]

I would love to be able to do this:

#[derive(Display)]
#[display("{major}.{minor}.{patch}")]
pub struct Version {
    major: usize,
    minor: usize,
    patch: usize,
}

instead of

#[derive(Display)]
#[display(fmt = "{}.{}.{}", major, minor, patch)]
pub struct Version {
    major: usize,
    minor: usize,
    patch: usize,
}

thiserror allows the first example, so it should be possible to be implemented.

[JelteF]

I would definitly like to have this feature, feel free to open a PR implementing it.

[tyranron]

@JelteF I believe this has been fully covered by #182