Add a script to test the image output from NodeJS

package.json

@@ -14,6 +14,7 @@
     "lodash": "~3.7.0"
   },
   "devDependencies": {
+    "canvas": "1.2.7",
     "jison": "0.4.13"
   },
   "scripts": {

test/nodejs.test.js

@@ -0,0 +1,26 @@
+// Writes a testing PNG diagram to the standard output
+// Usage: node nodejs.test.js > piracy.png
+var Canvas = require('canvas'),
+    nomnoml = require('../dist/nomnoml'),
+    canvas = new Canvas(640, 480),
+    source = '\
+      [Pirate|eyeCount: Int|raid();pillage()|\n\
+          [beard]--[parrot]\n\
+          [beard]-:>[foul mouth]\n\
+      ]\n\
+      \n\
+      [<abstract>Marauder]<:--[Pirate]\n\
+      [Pirate]- 0..7[mischief]\n\
+      [jollyness]->[Pirate]\n\
+      [jollyness]->[rum]\n\
+      [jollyness]->[singing]\n\
+      [Pirate]-> *[rum|tastiness: Int|swig()]\n\
+      [Pirate]->[singing]\n\
+      [singing]<->[rum]\n\
+      \n\
+      [<start>st]->[<state>plunder]\n\
+      [plunder]->[<choice>more loot]\n\
+      [more loot]->[st]\n\
+      [more loot] no ->[<end>e]\n';
+nomnoml.draw(canvas, source);
+canvas.pngStream().pipe(process.stdout);