Now only show 5 latest news in the home page, and put all the news in
the new page.
Change the css of news to the same as the publication.

1. Add one field, parent_menu, which should have the same name as the folder name (case insensitive). For menus has the same parent_menu are supposed to have the same menu_order.
 2. Change the way to generate navigator. Now it traverses the menu_order. If it is list of menu where the first element has parent_menu, it will generate a pop-up parent menu with a list of nav. Otherwise it will generate nav as before.

* People may be assigned to multiple research projects.
* Plugin for advanced filter expressions (see also
  https://github.com/jekyll/jekyll/pull/4478)