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.
After a long IRC discussion, it was decided that the use of direct
filepaths instead of the module is a more pure form of testing ,
although it may provide less overall coverage than the mixed integration
style imports used previously.
This will need to be remedied by further integration testing in
/test/integration.
