Add new favicon for v4 Middleman

https://trello.com/c/UN6YcgpO
Add links to navigation through pages

* Add links to docs
* Add links to external `middleman-directory` project
Add better Middleman logo SVG

* Replace SVG
* Set size limit for SVG
Connect sites using Middleman page to rest of website

* Add styles to site built but need to fix sticky
* Modify sticky sidebar by using fixed widths
* Rename `waypoints` tag class to `aside.sidebar-container`
* Refactor `#toc` into separate `sidebar` file
* Layout is *not responsive*
* Use new syntax for symbols
Fix syntax in config with hash rocket

* Use correct syntax
Replace second introduction item with illustration