Restructured the documentation.

docs/api.md

docs/api_reference.rst

docs/archive.rst

docs/client/client.rst

docs/dev/dev_guidelines.rst

docs/developers.md

docs/index.rst

docs/metainfo.rst

docs/normalizer.rst

docs/oasis.rst

docs/ops/oasis.rst

docs/ops/ops.rst

docs/parser.md

docs/python_reference.rst

docs/upload.rst

nomad/parsing/file_parser/README.md

nomad/parsing/file_parser/text_parser.py

nomad/units/__init__.py

nomad/utils/__init__.py

nomad/utils/structlogging.py