examples/ct: separate out MerkleTreeLeaf building
examples/ct: separate out MerkleTreeLeaf building

RJPercival/certificate-transparency-go,google/certificate-transparency-go,google/certificate-transparency-go,RJPercival/certificate-transparency-go,daviddrysdale/certificate-transparency-go,daviddrysdale/certificate-transparency-go,daviddrysdale/certificate-transparency-go,RJPercival/certificate-transparency-go,google/certificate-transparency-go