[WIP] Add QCQMC code and notebooks.

[fdmalone]

• Add existing code and notbooks to recirq
• Enable testing
• Add notebook which pulls Zenodo repo and reproduced paper results
• Add README

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[fdmalone]

cc @linusjoonho

[fdmalone]

I will split this up into ~ 5 PRs. This is the final state roughly with the tests passing locally on my machine.

[fdmalone]

[mpharrigan]

Make sure to add a new directory to docs/qcqmc with a file index.md that gives a brief introduction to the paper/experiment this code was used for and crucially has a link to the paper itself

[fdmalone]

closing this following #357. Phew. @wjhuggins please update as appropriate for better docs around shadow tomography.