Cleanup a bit

docs/assets/application.css

docs/images/autocomplete_new_button.png

docs/images/autocomplete_new_doubletap.png

docs/images/autocomplete_new_prefix.png

docs/images/autocomplete_old.png

docs/images/message_init.png

docs/images/message_setup.png

docs/index.md

docs/protocol/layers/message.md

docs/usage/faq.md

docs/usage/upgrade_guide.md

mkdocs.yml