Macro nova::newtype

macro_rules! newtype {
    (@ __impl $ty : path => $name : ident) => { ... };
    (@ __prefix $($tokens : tt) +) => { ... };
    ($ty : path => pub $name : ident) => { ... };
    ($ty : path => pub($($vis : tt) +) $name : ident) => { ... };
    ($ty : path => $name : ident) => { ... };
}

Create a clonable newtype for a given type and name.