Proto commits in tensorflow/quantum

These 4 commits are when the Protocol Buffers files have changed:

Commit:09ba5d3
Author:Antoine (Tony) Bruguier
Committer:GitHub

Implement serialization logic for ProjectorSums. (#623) * Serialize Projector Sums * nits * Use Boolean to encode the basis state * Address review comments

The documentation is generated from this commit.

Commit:534f65d
Author:MichaelBroughton
Committer:GitHub

Pulled out Cirq proto dependency. (#590) * Pulled out Cirq proto dependency. * format. * remove cirq from WORKSPACE.

Commit:d758f26
Author:Antonio Martinez

Cleared room for examples

This commit does not contain any .proto files.

Commit:ad4f7c9
Author:Michael Broughton

Initial copy from staging.