Function init_external 

pub unsafe extern "C" fn init_external(
    context: *mut c_context,
    value: *mut value,
    val: *mut ExternalValue,
) -> err

@brief Set an external value @ingroup value_create @param[out] context Optional, stores error information @param[out] value Nix value to modify @param[in] val the external value to set. Will be GC-referenced by the value. @return error code, NIX_OK on success.