[PATCH 0 of 2] Enhanced website navigation with 2-level menu and directive search

[Liam Crilly]

Hello! First-time posting here...

This patch series applies to the nginx.org repo. A video preview of the
changes can be seen at https://youtu.be/-XcBIfTqdxc 

Patch 1 adds a search* box below the logo with the goal of helping users
jump to the documentation for a specific directive or variable. It simply
constructs a nginx.org/r/... URI (there is no dynamic content or JavaScript
here). A corresponding location block is required in nginx.conf:
location = /s {
    rewrite ^ /r/$arg_q;
}

* it is not really a search :)

Patch 2 modifies the layout of the menu navigation with the goal of highlighting
the njs and Unit projects. These are significant NGINX projects which are too easy
to overlook through natural site navigation. Summary of changes:
 - A two-level heirarchy organises content into sections for nginx, other
   nginx projects, and information
 - The "projects" of njs and unit are moved up, to a more prominent position
 - News is moved lower down, to the "info" section. A third menu level
   contains the individual years so that the top of the menu is always the
   same, regardless of which page you are on.
 - Links to external sites are indicated by a right-arrow character


Cheers,
Liam.