Use jimp instead of lwip for image processing

Jimp does not install on recent versions of NodeJS because of changes
in the bundled version of zlib. Jimp is a pure JS replacement.

lib/screenshotHandler.js

@@ -1,5 +1,5 @@
 var debug       = require('debug')('ylt:screenshotHandler');
-var lwip        = require('lwip');
+var Jimp        = require('jimp');
 var tmp         = require('temporary');
 var Q           = require('q');
 var fs          = require('fs');
@@ -57,7 +57,7 @@ var screenshotHandler = function() {
     this.openImage = function(imagePath) {
         var deferred = Q.defer();
 
-        lwip.open(imagePath, function(err, image){
+        Jimp.read(imagePath, function(err, image){
             if (err) {
                 debug('Could not open imagePath %s', imagePath);
                 debug(err);
@@ -76,7 +76,7 @@ var screenshotHandler = function() {
     this.resizeImage = function(image, newWidth) {
         var deferred = Q.defer();
 
-        var currentWidth = image.width();
+        var currentWidth = image.bitmap.width;
         var ratio = newWidth / currentWidth;
 
         image.scale(ratio, function(err, image){
@@ -101,7 +101,7 @@ var screenshotHandler = function() {
         var deferred = Q.defer();
 
         // Create a canvas with the same dimensions as your image:
-        lwip.create(image.width(), image.height(), 'white', function(err, canvas){
+        new Jimp(image.bitmap.width, image.bitmap.height, 0xFFFFFF, function(err, canvas){
             if (err) {
                 debug('Could not create a white canvas');
                 debug(err);
@@ -109,7 +109,7 @@ var screenshotHandler = function() {
                 deferred.reject(err);
             } else {
                 // Paste original image on top of the canvas
-                canvas.paste(0, 0, image, function(err, image){
+                canvas.composite(image, 0, 0, function(err, image){
                     if (err) {
                         debug('Could not paste image on the white canvas');
                         debug(err);
@@ -131,7 +131,7 @@ var screenshotHandler = function() {
     this.toBuffer = function(image) {
         var deferred = Q.defer();
 
-        image.toBuffer('jpg', {quality: 90}, function(err, buffer){
+        image.quality(90).getBuffer(Jimp.MIME_JPEG, function(err, buffer){
             if (err) {
                 debug('Could not save image to buffer');
                 debug(err);
@@ -143,7 +143,7 @@ var screenshotHandler = function() {
             }
         });
 
-        return deferred.promise;        
+        return deferred.promise;
     };
 
 
@@ -167,4 +167,4 @@ var screenshotHandler = function() {
     };
 };
 
-module.exports = new screenshotHandler();
+module.exports = new screenshotHandler();