Improved API, added first performance test

tests/perf.js

@@ -0,0 +1,42 @@
+var sharp = require("../index");
+var imagemagick = require("imagemagick");
+var assert = require("assert");
+
+// http://www.flickr.com/photos/grizdave/2569067123/
+var input = __dirname + "/2569067123_aca715a2ee_o.jpg";
+var output = __dirname + "/output.jpg";
+
+var width = 640;
+var height = 480;
+
+// imagemagick
+var time = process.hrtime();
+imagemagick.resize({
+  srcPath: input,
+  dstPath: output,
+  quality: 0.75,
+  width: width,
+  height: height
+}, function(err) {
+  if (err) {
+    throw err;
+  }
+  var diff = process.hrtime(time);
+  imagemagickTime = diff[0] * 1e9 + diff[1];
+  console.log("imagemagick took %d nanoseconds", imagemagickTime);
+
+  // sharp
+  time = process.hrtime();
+  sharp.crop(input, output, width, height, function(err) {
+    if (err) {
+      throw err;
+    }
+    diff = process.hrtime(time);
+	var sharpTime = diff[0] * 1e9 + diff[1];
+    console.log("sharp took %d nanoseconds", sharpTime);
+
+	// diff
+	assert(sharpTime < imagemagickTime, "sharp was blunt");
+	console.log("sharp was %d%% faster", (imagemagickTime - sharpTime) / imagemagickTime * 100);
+  });
+});