An ECKey is a composition of a private key (D), a public key (Q) and its
compression flag.
These functions gave the impression of serialization of this
composition, when really they only serialized `D`.
They have therefore been removed in favour of always using a sane
serialization format (WIF) that matches the needed behaviour.
If a user needs the previous functionality, simply use `privKey.D.*`
instead of `privKey.*`, as BigInteger supports `*Buffer/*Hex` functions
as expected.
The use of fixtures allows for more behavioural driven tests and simpler
addition of more test cases in future.
However, as ECPubKey is just a wrapper around other strenuously tested
modules, the test data is currently limited to testing a subset of the
total wrapper.
This should probably be done better by using mocked out modules instead.
The introduction of these two functions allow for the all the network
related code to be eventually removed from Transaction and Script.
Previously the result for non-standard transactions was undefined
behaviour. This change mandates that an exception is thrown if a
non-standard transaction is input.
