add interface for zero knowledge interval proof

[omershlo]

prove that a pedersen commitment is to a value a<x<b.
If b-a is a power of 2 this can be done non interactively with only one range proof assuming the:

1. prover commits to a value a<x<b
2. prover generates a pedersen commitment to a value a
3. prover generates a range proof to commitment that is commitment from 1 minus commitment from 2
4. prover sends range proof together with the opening of the commitment from 2