Hivemind

This release adds several new features:
* Client-only averaging in AllReduce (176)
* Expert learning rate scheduling (196)
* Quantile compression (182)

Also, this release contains the following fixes and improvements:
* Fix scalar deserialization (190)
* Extract expert-specific methods from DHT (192)

This release fixes several known bugs and security vulnerabilities:
* Copytree implementation for py37 compatibility (162)
* Remove pickle.loads in Averager (160)
* Support edge cases for DHT key/subkey/value (167)
* Fix the remaining tests for py37 (166)
* Move Averager metadata serialization out of user scope (168)
* Handle edge cases in DecentralizedAverager (171)
* Fix a typo in quickstart.md (174)
* Serialize DHTID source with msgpack (172)
* Move CLI server launch script to hivemind/hivemind_cli (173)

* Implement DecentralizedAverager for averaging model parameters & statistics across DHT peers (119 123 134 140 141)
* Accelerate RemoteMixtureOfExperts beam search with new key structure (97 101 103 109)
* Implement lossy compression algorithms for tensors (102 106 112)
* Detect anomalies in RemoteMixtureOfExperts (132)
* Configure gRPC channels for long-term stability (129 131)
* Load expert checkpoints on server startup (138)
* Support attention mask in example TransformerEncoder layer (126)
* Add the contribution guide (156)

Bugfixes:
* Fix wrong getattr in hivemind.Server (122)

Enhancements:
* Suport python3.9 and torch1.7 (142)
* Blacklist nonresponsive peers with exponential backoff (114)
* Reuse grpc channels between calls (120)
* Verify DHT peer accessibility and local clock (137)
* Improve logging, remove duplicate log entries (135)
* Improve test coverage (116)

* Remove name property from all asyncio tasks (compatibility with python3.7)

Minor update:
* you can now create minimalistic hivemind server via ./script/run_server.py Vsevolod-pl
* ./script/run_server.py can now sample experts from a pre-defined grid, e.g. expert.[0:256].[0:256]
* added quickstart tutorial justheuristic

* Speed up tests, shutdown threads in server via threading.Event
* Compile protobuf in setup.py
* Update circleci pipelines
* Update RTD pipeline
* Refactor custom build_ext into install and develop