refactor: Move SCSS functions and abstract build data retrieval

I've moved the SCSS functions file into the `scripts` directory where I think it makes a bit more
sense. I've also abstracted most of the functionality from it so I can also use it in
`semantic-release`'s preparation step.

scss/nes.scss

@@ -1,7 +1,9 @@
 @charset "utf-8";
 
 /*****************************************************************************\
-#{version()}
+  NES.css Framework
+  Version: development
+#{build-data()}
 \*****************************************************************************/
 
 @import "base/_index.scss";