Macro wrap

macro_rules! wrap {
    ($( #[ $attr:meta ] )* struct $outer:ident($inner:ty);) => { ... };
    ($( #[ $attr:meta ] )* pub struct $outer:ident($inner:ty);) => { ... };
    ($inner:ty, $outer:ty) => { ... };
}

Implement bidirectional From and on-way AsRef/AsMut for two types, $inner and $outer.

sp_application_crypto::wrap! {
    pub struct Wrapper(u32);
}