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.

scripts/getBuildData.js

@@ -0,0 +1,26 @@
+const git = require('git-rev-sync'); /* eslint-disable-line import/no-extraneous-dependencies */
+
+module.exports = (isCompiled = false) => {
+  let buildData = '';
+
+  if (git.branch() !== 'master') {
+    buildData += '\n';
+
+    if (isCompiled) {
+      buildData += `
+        Build Date: ${(new Date()).toISOString()}
+        Node Version: ${process.version}`;
+    }
+
+    buildData += `
+      Branch: ${git.branch()}
+      Commit: ${git.long()}`;
+
+    if (process.env.CIRCLECI) {
+      buildData += `
+        Build Number (CircleCI): ${process.env.CIRCLE_BUILD_NUM}`;
+    }
+  }
+
+  return buildData.replace(/\n/, '').replace(/^  +/gm, '  ');
+};

scripts/scssFunctions.js

@@ -0,0 +1,7 @@
+const { types } = require('node-sass'); /* eslint-disable-line import/no-extraneous-dependencies */
+
+const getBuildData = require('./getBuildData');
+
+module.exports = {
+  'build-data()': () => types.String(getBuildData(true)),
+};