Bump version to 2.12.0

Bump version to 2.11.0

Bump version to 2.10.0

Bump version to 2.9.1

Bump version to 2.9.0

Update changelog for 2.8.0

 Bump version to 2.7.2 for a patch release (rigetti#901)

* Add back readout_symmetrize for deprecation

* Bump version to 2.7.2

* Update the changelog for v2.7.2

* Hit an undersampling error, so bumping some shots

Bump version to 2.7.1 for a patch release (rigetti#899)

* Considerably reduce sampling in operator estimation UTs

* Make stderr operator estimation change backwards compatible

* Make tomographyexperiment qubits change backwards compatible

* Update the build badges in the README

* Bump version to 2.7.1

* Update the changelog for v2.7.1

Bump version to 2.7.0 and update changelog

Bump version to 2.6.0 (rigetti#868)