Currently we use `u8` for key type but it was pointed out that we should
be using a `u64` and encoding it as a compact type. The reason our code
works now is because the compact type encoding for a `u8` (less than
253) is the same as for a `u8`.
This breaks the `serde` impl, as shown by changes to the regression tests.
In order that we can safely change/maintain de/serialization code we
need to have regression tests with hard coded serializations for each
type that implements serde.
It is enough to test a single serde data format, use JSON for `opcodes`
and bincode for other types.
Do regression testing in a newly added `tests` module.
Tobin C. Harding