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/functions.js

@@ -1,28 +0,0 @@
-const git = require('git-rev-sync'); /* eslint-disable-line import/no-extraneous-dependencies */
-const { types } = require('node-sass'); /* eslint-disable-line import/no-extraneous-dependencies */
-
-module.exports = {
-  'version()': () => {
-    const packageData = require('../package.json'); /* eslint-disable-line global-require */
-
-    let buildData = `
-      NES.css Framework
-      Version: ${(git.branch() === 'develop') ? 'development' : `v${packageData.version}`}
-    `;
-
-    if (git.branch() !== 'master') {
-      buildData += `
-        Build Date: ${(new Date()).toISOString()}
-        Node Version: ${process.version}
-        Branch: ${git.branch()}
-        Commit: ${git.long()}`;
-    }
-
-    if (process.env.CIRCLECI) {
-      buildData += `
-        Build Number (CircleCI): ${process.env.CIRCLE_BUILD_NUM}`;
-    }
-
-    return types.String(buildData.replace(/\n/, '').replace(/^  +/gm, '  '));
-  },
-};

scss/nes.scss

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