"noise" option

This release enables noisy simulation with a depolarization parameter set by the "noise" option, for every single gate in a circuit.

Cases of circuits with mid-circuit measurement have also been debugged.

Full Changelog: v0.7.0...v0.8.1

sha1sum results:
9d3983c758c6039bed7fd996fa44a83eca77cc20 cirqqrack-0.8.1-py3-none-any.whl
dc15c83b1331d7a6abf2048d95fed25dd06baebf cirqqrack-0.8.1.tar.gz