pages: browser metadata + root `_browser`: - the `_browser` directory can now be put in root of a site `pages` directory, it will then include modules for the whole website - in `_browser` directories (notably the root one), a `browser_meta.json` file can be put to specify settings for a browser engine - pathlib.Path is now used LiberviaRootResource.site_path - introduced some type hints - task_brython copy modules in root `_browser` to build_path root. - minimal python version is now 3.7 due to type hints