Release notes for Genode 13.02
release notes: aggregate more git commit messages
release notes: document structure
release notes: audio, microblaze, okl4
release notes: terminal_mux
release notes: device drivers, 3rd-party libraries
release notes: timer, fs_rom, file-system
release notes: loader, nic_bridge, nitpicker
release notes: signal, unified APIs, base libs
release notes: failsafe, synchronization