fix the serialization interface between bls and zexe

[drskalman]

zexe now uses serde like serialization as zkcrypto was using a EncodedPoint trait. We need to either adapt or migrate to new serialization or the tests won't pass.

[drskalman]

I spent the first part of the week to implement an adapter so I can keep @burdges 's macros intact. Then on @burdges 's advice I reimplemented the macro using the new interface. Note that we couldn't derive Canonical(De)Serialize on Signature and PublicKey because ProjectiveCurve does not implement those traits.

[drskalman]

Moved zbls macros to new serialization paradaigm. Now the tests also compile but two fails: da4ce55,

running 4 tests
test single::tests::single_messages ... FAILED
test delinear::tests::delinearized ... ok
test distinct::tests::distinct_messages ... ok
test bit::tests::proofs_of_possession ... FAILED

Will investigate in aother issue.