Merge branch 'release-0.2.1'

.gitlab-ci.yml

CMakeLists.txt

Makefile

RELEASE_GUIDELINES.md

conanfile.py

doc/CHANGELOG.md

include/caosdb/logging.h

requirements.txt

src/caosdb/connection.cpp

src/caosdb/file_transmission/download_request_handler.cpp

src/caosdb/file_transmission/upload_request_handler.cpp

src/caosdb/transaction.cpp

src/caosdb/unary_rpc_handler.cpp

test/test_transaction.cpp