* adding new avatars by David Revoy
* replacing old avatars to test
TODO: add a settings to choose between legacy and new avatars.
TODO: generate a bot avatar.
* Adding a help button on top of the chat, that links to the online documentation on frama.io.
* Replaced github.io documentation links by frama.io documentation.
* Adding links to the documentation in the diagnostic tool.
Moving `public/images` dir to `assets/images`, because it conflicts with gitlab CI/CD for documentation.
Moving `assets/styles.css` to `assets/styles/styles.css`.
Related to #117.
