Cirq v0.12 release

[Michael Broughton]

Dear Cirq Users,

We have just released Cirq minor version v0.12.0.

Some of the bigger highlights of this release are:

1. New vendor modules:

You can now install any vendor specific package by running `pip install cirq-***` where *** can be any one of "web", "aqt", "core", "google", "rigetti", "ionq", and "pasqal".

2. New optimizations techniques for sqrt-iswap gates.

3. 3D Circuit visualization in `cirq-web`.

For a complete list of features, fixes and breaks for this release, check out: https://github.com/quantumlib/Cirq/releases/tag/v0.12.0

To install this upgrade run `pip install cirq==0.12.0`

Thank you so much to everyone who helped make this release happen: Adam Zalcman, Ana Sofia Uzsoy, Antoine (Tony) Bruguier, Balint Pato, Bicheng Ying, Casey Duckering, Craig Gidney, Dax Fohl, Dmytro Fedoriaka, Doug Strain, Eric Hulburd, Jannes Stubbemann, Laurent AJDNIK, madcpf, Malice, Mark Daoust, Martin Leib, Matthew Harrigan, Matthew Neeley, Michael Broughton, MichaelBroughton, Nathanael Thompson, Niko Savola, Noureldin, Orion Martin, Ryan LaRose, Seun Omonije, Smit Sanghavi, Tanuj Khattar, Victory Omole and Wojciech Mruczkiewicz.

Cheers,

Michael