Macro impl_writeable_tlv_based

macro_rules! impl_writeable_tlv_based {
    ($st: ident, {$(($type: expr, $field: ident, $fieldty: tt)),* $(,)*}) => { ... };
}

Implements Readable/Writeable for a struct storing it as a set of TLVs If $fieldty is required, then $field is a required field that is not an Option nor a Vec. If $fieldty is (default_value, $default), then $field will be set to $default if not present. If $fieldty is option, then $field is optional field. If $fieldty is optional_vec, then $field is a Vec, which needs to have its individual elements serialized. Note that for optional_vec no bytes are written if the vec is empty

For example,

struct LightningMessage {
	tlv_integer: u32,
	tlv_default_integer: u32,
	tlv_optional_integer: Option<u32>,
	tlv_vec_type_integer: Vec<u32>,
}

impl_writeable_tlv_based!(LightningMessage, {
	(0, tlv_integer, required),
	(1, tlv_default_integer, (default_value, 7)),
	(2, tlv_optional_integer, option),
	(3, tlv_vec_type_integer, optional_vec),
});