Add png-benchmark demo

Author: blikblum

demo/png-benchmark.js

@@ -0,0 +1,33 @@
+const PDFDocument = require('../');
+const fs = require('fs');
+
+const doc = new PDFDocument();
+
+// files with alpha channel -> uses zlib.deflate
+const files = [  
+  'test.png',
+  'test3.png'
+];
+
+const filesData = files.map(fileName => {
+  return fs.readFileSync(`images/${fileName}`);
+});
+
+const iterationCount = 100;
+
+console.time('png-bench')
+
+for (let i = 0; i < iterationCount; i++) {  
+  filesData.forEach(data => {
+    doc.image(data)
+    doc.addPage()
+  })
+}
+
+doc.on('data', () => {})
+
+doc.on('end', () => {  
+  console.timeEnd('png-bench');
+});
+
+doc.end();