New protocol: Weak String Erasure

For this new release, we implemented the Weak String Protocol described at Weak String Erasure.

It is based on Alice sending qubits encoded in BB84 states and Bob measuring them at the other end. When Bob and Alice share the same basis they are garanteed to get the same results, yet if Alice is giving her preparation basis to Bob, but Bob does not give the measurement basis to Alice she cannot know which bits they have in common. The protocol works because there is a bound on the decoherence time of quantum memories that Bob could try to use for cheating.