Add performance test.

Author: samccone

perf/index.js

@@ -0,0 +1,11 @@
+const fs = require('fs');
+const path = require('path');
+const unesc = require('../dist/util/unesc');
+const selectors = fs.readFileSync(path.join(__dirname, 'selectors.css'), 'utf-8').split('\n');
+
+for (let i = 0; i < 100; i++) {
+    for (let s of selectors) {
+        unesc(s);
+    }
+}
+