Replace proof Verification by go-ethereum impl

[ed255]

• Remove the custom Merkle Patricia Trie proof verification
  implementation
• Remove the custom RLP encoding/decoding implementation
• Use the Merkle Patricia Trie proof verification function from
  go-ethereum
  • This adds support to all types of non-existence proofs
• Use the RLP encoding/decoding functions from go-ethereum
• Add BytesHexQuantityBytes and SliceData to abstract encoding of QUANTITY and slices of bytes in
  the StorageProof types

[p4u]

It would be nice to add some extra test to this "new code". We could use the Proofs hardcoded on this test from vocdoni-node
https://github.com/vocdoni/vocdoni-node/blob/master/vochain/proof_test.go#L574

What do you think @ed255?

[ed255]

It would be nice to add some extra test to this "new code". We could use the Proofs hardcoded on this test from vocdoni-node
https://github.com/vocdoni/vocdoni-node/blob/master/vochain/proof_test.go#L574

What do you think @ed255?

I've added a new commit which will:

• Add proofs from https://github.com/vocdoni/vocdoni-node/blob/5b292fc7e74327f0127908636072482660b060b2/vochain/proof_test.go#L574
• Add a minime storage proof of non-existence that couldn't be verified with the previous VerifyProof implementation.

I had to edit the value fields from https://github.com/vocdoni/vocdoni-node/blob/5b292fc7e74327f0127908636072482660b060b2/vochain/proof_test.go#L574 because they were even-length hex strings (I added a padding 0). How where those proofs generated?

[p4u]

RLP encoding can produce even-length hex strings, i.e 0x0 means "null" for RLP. So the Marshaling/Unmarshaling should take this into account, instead of using hex.Decode() you probably want to use some specific RLP function. Or you can just list the cases where the length can be even and modify the original hex string accordingly.

I.e https://github.com/vocdoni/storage-proofs-eth-go/blob/master/ethstorageproof/ethstorageproof.go#L339

[p4u]

Whenever this is addresses, ping me please :)

[p4u]

LGTM now, just minor comments. You can address them or let it for a future PR.

Please, "rebase and merge" yourself.