Cicada-mpc

* SocketCommunicator.run() would sometimes hang returning results from large numbers of players.
* Sped-up regression tests significantly by removing unnecessary redundancy.
* Began formally testing Cicada with Python 3.8 and 3.10.
* Added user guide sections on Shamir sharing and fault recovery.
* Reorganized SocketCommunicator statistics, and added statistics organized by message type.
* Added the cicada-perf command for benchmarking communications.
* Added `indices` and `threshold` properties to ShamirBasicProtocol and ShamirProtocol.
* SocketCommunicator setup didn't always use the correct rank and name in log output.
* Fixed a problem with the way thresholds are constrained in ShamirProtocol.
* Explicitly specify process names for debugging with SocketCommunicator.run().
* Removed obsolete code.

* A botched merge left some changes out of the 0.5.0 release.

* ShamirProtocol provides the same operations as AdditiveProtocol.
* New ShamirBasicProtocol provides a subset of operations, but with relaxed constraints on share degree.
* Reduced per-message SocketCommunicator overhead.
* SocketCommunicator.run, SocketCommunicator.shrink, and SocketCommunicator.split support Unix domain sockets.
* Rewrite the SocketCommunicator.shrink implementation for simplicity.
* SocketCommunicator can raise exceptions while sending.
* Rewrote the SocketCommunicator message queue for reduced resource consumption and greater flexibility.
* Point-to-point SocketCommunicator operations support user-defined message tags.
* Reduced the number of coordinating messages during logging.
* Many improvements in library logging output.
* Added a user guide article on logging.

* SocketCommunicator supports TLS encryption.
* SocketCommunicator supports Unix domain sockets.
* Moved SocketCommuniator initialization into a separate module.
* Fixed problems with AdditiveProtocol.private_public_power.
* Reduced default log output, and made log output more consistent.
* Raise an exception trying to use a communicator that's been freed.
* Removed the cicada.bind module.

* Improved code coverage from 80% to 95%.
* Greatly improved SocketCommunicator startup behavior.
* SocketCommunicator can choose random ports for players other than root.
* Made SocketCommunicator.override() more flexible.
* Fixed a bug in AdditiveProtocol.zigmoid().
* Eliminated warnings waiting for interactive user input.
* cicada.interactive.secret_input() just prompts for input.
* Created new `cicada` command to replace `cicada-exec`, which is deprecated.

* Replaced NNGCommunicator with SocketCommunicator, for vastly improved reliability.
* Added ReLU function.
* Added absolute value function.
* Added bit decomposition function.
* Added division function.
* Added equality comparison function.
* Added floor function.
* Added less-than-zero function.
* Added logical negation function.
* Added min and max functions.
* Added multiplicative inverse function.
* Added zigmoid function.
* Added many new documentation topics, including communication patterns, random seeds, timeouts, and working with multiple communicators.
* Switched to Github Actions for continuous integration.
* Improved code test coverage.