DOC: Removed (partly migrated) documentation directory `/doc/`

CHANGELOG.md

doc/Authentication.md

doc/Datatype.md

doc/Entity.md

doc/FileServer.md

doc/Message.md

doc/Paging.md

doc/Query.md

doc/User_Administration.md

doc/devel/Benchmarking.md

doc/devel/Development.md

doc/devel/Logging.md

doc/faq.md

src/doc/CaosDB-Query-Language.md

src/doc/FAQ.rst

src/doc/conf.py

src/doc/development/benchmarking.md

src/doc/development/benchmarking.rst

src/doc/development/devel.rst

src/doc/development/logging.rst