New release v2.6

- Make the checker command line reactive to custom variables changes
- Make `flycheck-grammalecte-setup` idempotent
- Improve demo startup
- Change how demo dependencies are setup

- Correctly report the grammalecte package install path
- Trigger a flycheck update after fixing an error
- Do not report errors for bullet lists in org-mode

- Update README.org for modern setup
- Remove liberapay link from README.org
- Add a no AI policy in CONTRIBUTING.org and a link to it in README.org
- Remove deprecated MANUAL_INSTALL.org file
- Add comments for `flycheck-grammalecte-filters-by-mode` patterns

- Use `bind-key` instead of `keymap-set`
- Remove `seq` dependency from grammalecte.el
- Stop byte-compiling elisp files