Convert `Vec` de/serialization impl to a macro and impl for tuples

Convert `Vec` de/serialization impl to a macro and impl for tuples

...to make it easier to add new implementations and implement it
for all tuples which implement `Readabe` + `Writeable`. Note that
we don't want to just convert to a blanket implementation as we'd
really like to keep our optimized `Vec<u8>` wrapper or we'll end
up spinning way too much when writing vecs of bytes.