In BIP0032, m is used as a variable for the root extended key. It is not
meant to be used as a constant prefix when serializing paths.
Update the DerivationPath parser to no longer require the m prefix.
Remove the m prefix from the unit tests and the bip32, ecdsa-psbt,
and taproot-psbt examples.
close#2449
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.
josibake
Subhradeep Chakraborty
Tobin Harding