Emit events via npm module for certain page loading milestones

[macbre]

Emit milestone event via npm module on:

• first byte of content response received
• last byte of content response received
• onDOMReady event fired
• window onload event fired

[macbre]

phantomas/examples$ DEBUG=phantomas:milestone ./npm.js 
phantomas v0.12.1 loaded from /home/macbre/github/phantomas/lib
Running phantomas: pid 24037
Loading progress: 10%
  phantomas:milestone timeToFirstByte: 175 ms +0ms
timeToFirstByte at 175 ms
  phantomas:milestone timeToLastByte: 225 ms +1ms
timeToLastByte at 225 ms
  phantomas:milestone onDOMReadyTime: 1 ms +0ms
onDOMReadyTime at 1 ms
Loading progress: 36%
Loading progress: 42%
Loading progress: 62%
Loading progress: 100%
  phantomas:milestone windowOnLoadTime: 354 ms +353ms
windowOnLoadTime at 354 ms