New verify and create functions are needed for NamespaceMerkleTreeInclusionProof.

A new verify function is needed to verify a single share via a [NamespaceMerkleTreeInclusionProof](https://github.com/celestiaorg/celestia-specs/blob/master/src/specs/data_structures.md#namespacemerkletreeinclusionproof) defined in celestia-specs.

This function should take (i) a NMT root of type namespace.IntervalDigest, (ii) a hash function of type hash.Hash, (iii) a proof of type NamespaceMerkleTreeInclusionProof and (iv) a share of type [Share](https://github.com/celestiaorg/celestia-specs/blob/master/src/specs/data_structures.md#share), and output a boolean and an error that is (true, nil) if the share is committed by the NMT root inside the NMT and the proof of type NamespaceMerkleTreeInclusionProof is correct.

Similarly, a new create function is needed to create a [NamespaceMerkleTreeInclusionProof](https://github.com/celestiaorg/celestia-specs/blob/master/src/specs/data_structures.md#namespacemerkletreeinclusionproof). This function should take the index of the [Share](https://github.com/celestiaorg/celestia-specs/blob/master/src/specs/data_structures.md#share) inside the NMT and output the NamespaceMerkleTreeInclusionProof corresponding to the share.