Macro impl_dlc_writeable_external 

macro_rules! impl_dlc_writeable_external {
    ($st: ident $(< $gen: ident $(< $gen2: ident >)?> )? , $name: ident, {$(($field: ident, $fieldty: tt)), *} ) => { ... };
}

Implements the lightning::util::ser::Writeable trait for a struct external to this crate.