[docs] split development docs

docs/designdocs/index.rst

docs/hacking/architecture.rst

docs/hacking/contributing.rst

docs/hacking/devenv.rst

docs/hacking/index.rst

docs/hacking/privileges.rst

docs/hacking/release.rst

docs/hacking/uidev.rst

docs/installation/index.rst

docs/testing/index.rst

release-notes.rst