adding a MerkleTree serializer

[themighty1]

Hi, currently rs-merkle only supports serializing MerkleProof types.
In our use case we build a MerkleTree and want to store it on disk to generate proofs at a later time. Would you be interested in a PR adding a serialize/deserialize methods to MerkleTree?

[antouhou]

Hey @themighty1 ! I sure would!

[enginefuture]

same problem

[themighty1]

@antouhou , there is a PR linked to above which addresses this issue.