Add collision probabilities for MIPSHash and SignALSH

[kernelmethod]

There isn't currently an implementation of collision_probability or single_hash_collision_probability for either MIPSHash or SignALSH. These should be added to the LSH module and tested in test/hashes/test_mips_hash.jl and test/hashes/test_sign_alsh.jl.

References for collision probabilities:

• MIPSHash: https://arxiv.org/abs/1405.5869
• SignALSH: https://arxiv.org/abs/1410.5410v2