Added a prettier setup

.eslintignore

@@ -0,0 +1,2 @@
+unexpected-dom.js
+unexpected-dom.min.js

.eslintrc.js

@@ -0,0 +1,24 @@
+const config = {
+  extends: ['pretty-standard'],
+  plugins: ['import'],
+  rules: {
+    'import/no-extraneous-dependencies': [
+      'error',
+      {
+        devDependencies: ['**/test/**/*.js'],
+        optionalDependencies: false,
+        peerDependencies: false
+      }
+    ]
+  }
+};
+
+if (process.stdin.isTTY) {
+  // Enable plugin-prettier when running in a terminal. Allows us to have
+  // eslint verify prettier formatting, while not being bothered by it in our
+  // editors.
+  config.plugins.push('prettier');
+  config.rules['prettier/prettier'] = 'error';
+}
+
+module.exports = config;

.prettierignore

@@ -0,0 +1,3 @@
+package.json
+unexpected-dom.js
+unexpected-dom.min.js

.prettierrc

@@ -0,0 +1,3 @@
+{
+  "singleQuote": true
+}