cirq v1.3.0 release

[Doug Strain]

Dear Cirq Users, 

I am pleased to announce a new minor release for Cirq, version v1.3.0! The release is available on pypi, please install/upgrade via  pip install --upgrade cirq==1.3.0

This minor version Cirq release focuses on many bug fixes and performance improvements, as well as the graduation of cirq-ft into the qualtran repository.

Deprecation of cirq-ft

The newly created cirq-ft package (from 1.2.0) will be moving to its new home in the qualtran repository. Please pull from that repository to get all your fault-tolerant resource estimation goodness.

Qubit management
Two new qubit managers (GreedyQubitManager and SimpleQubitManager) can help manage creation and allocation of temporarily or borrowed ancilla qubits.

Performance improvements
Many minor performance improvements have been made over the past 6 months to help speed up troublesome corner cases, such as json serialization, transformers, circuit creation, and symbol resolution.  A classical simulator for simulating circuits without superposition (such as Toffoli, CNOT, X, SWAP, etc) has been added.

A Huge Thank You
Thank you to all our contributors for this release:

Andreas Bengtsson, Bram Evert, Cheng Xing, Doug Strain, Dripto Debroy, eliottrosenberg, Emilio Peláez, Fionn Malone, Jon Donovan, Jose Urruticoechea, Matthew Neeley, Nishna Aerabati, Nafay Najam, Noureldin, Ogah Jackreece Ejini, Pavol Juhas, richrines1, Ryan Hill, Sam Burdick, Sanuj Sharma, Seneca Meeks, Shef, Spencer Churchill, Suyash Damle, Tanuj Khattar, yinghui-hu, Yisu Peng

You can find the complete release notes at https://github.com/quantumlib/Cirq/releases/tag/v1.3.0