Add autoprefixer and postcss

Added:
- autoprefixer v10.3.4
- postcss v8.3.6

Changed:
- Node Sass options to pass source map to PostCSS.

build/styles.js

@@ -1,5 +1,7 @@
+import autoprefixer from 'autoprefixer';
 import fs from 'fs';
 import sass from 'node-sass';
+import postcss from 'postcss';
 import paths from '../mconfig.json';
 import message from './utils/message.js';
 import notification from './notification.js';
@@ -20,9 +22,11 @@ export function compileStyles() {
 
         sass.render({
             file: infile,
+            omitSourceMapUrl: true,
             outFile: outfile,
             outputStyle: 'compressed',
-            sourceMap: true
+            sourceMap: true,
+            sourceMapContents: true
         }, (err, result) => {
             if (err) {
                 message(`Error compiling ${name}.scss`, 'error');
@@ -35,19 +39,62 @@ export function compileStyles() {
                 return;
             }
 
-            fs.writeFile(outfile, result.css, (err) => {
+            fs.access(outfile, (err) => {
                 if (err) {
                     message(`Error compiling ${name}.scss`, 'error');
-                    message(err.formatted);
+                    message(err);
 
                     notification({
                         title:   `${name}.scss compilation failed 🚨`,
-                        message: `Could not save stylesheet to ${name}.css`
+                        message: err
                     });
                     return;
                 }
 
-                message(`${name}.css compiled`, 'success', timeLabel);
+                postcss([ autoprefixer ]).process(result.css, {
+                    from: outfile,
+                    to: outfile,
+                    map: {
+                        annotation: false,
+                        inline: false,
+                        sourcesContent: true
+                    }
+                }).then((result) => {
+                    result.warnings().forEach((warn) => {
+                        message(`Error prefixing ${name}.css`, 'error');
+                        message(warn.toString());
+                    });
+
+                    fs.writeFile(outfile, result.css, (err) => {
+                        if (err) {
+                            message(`Error compiling ${name}.scss`, 'error');
+                            message(err);
+
+                            notification({
+                                title:   `${name}.scss compilation failed 🚨`,
+                                message: `Could not save stylesheet to ${name}.css`
+                            });
+                            return;
+                        }
+
+                        message(`${name}.css compiled`, 'success', timeLabel);
+                    });
+
+                    if (result.map) {
+                        fs.writeFile(outfile + '.map', result.map.toString(), (err) => {
+                            if (err) {
+                                message(`Error compiling ${name}.scss`, 'error');
+                                message(err);
+
+                                notification({
+                                    title:   `${name}.scss compilation failed 🚨`,
+                                    message: `Could not save sourcemap to ${name}.css.map`
+                                });
+                                return;
+                            }
+                        });
+                    }
+                });
             });
         });
     });