build: Make build versions dynamic

Hehehehe, this is really cool. I've removed the hardcoded version number from `nes.scss` and
replaced it with a custom function. This function does all sorts of cool stuff.

1. **Injects the framework version from `package.json`
  This prevents us from having to inject the version number manually.
2. **Adds build info…**
  The branch that the CSS was built from, when it was built, what version of Node was used… All of the useful information that we could possibly provide. If it’s built on CircleCI, it even includes the build number.
3. **…but not too much build info**
  If the build is running against the `master` branch, we only inject the framework version. No need to bloat production builds with all the other junk. 😁

scss/nes.scss

@@ -1,8 +1,8 @@
 @charset "utf-8";
 
-/*!
-* NES.css v0.0.2(alpha)
-*/
+/*****************************************************************************\
+#{version()}
+\*****************************************************************************/
 
 @import "base/_index.scss";
 @import "utilities/_index.scss";