Add CMake support and enhance the getting started docs

- Add a root CMakeLists.txt defining an INTERFACE target.
- Add CMake, qpm, Git and download installation instructions.
- Add CMake and qmake integration instructions.
- Remove smooth scroll when navigating the docs.
- Add links validation to `npm run docs:link`.
- Reorganize the sidebar API Reference section.

docs/.vuepress/styles/index.styl

@@ -19,7 +19,7 @@ sup
     #main-title
         display none !important
 
-.content a code
+.page a code
     color $accentColor
 
 .navbar