Uses the pairing library written by ZCash project:
https://electriccoin.co/blog/pairing-cryptography-in-rust/

Originally pairing library, now renamed to bls12_381

To run the example tool:

  $ git clone https://github.com/narodnik/darktoken
  $ cd darktoken
  $ cargo build --examples
  $ cd target/debug/examples/
  $ ./darktoken help