Function encode_varule_to_box 

pub fn encode_varule_to_box<S: EncodeAsVarULE<T> + ?Sized, T: VarULE + ?Sized>(
    x: &S,
) -> Box<T>

Given an EncodeAsVarULE type S, encode it into a Box<T>

This is primarily useful for generating Deserialize impls for VarULE types