Supports PhantomJS/CasperJS

Hi, I just added some code to support PhantomJS/CasperJS.
Now, It works on both Headless Browser perfectly!



#### On PhantomJS
![PhantomJS Demo](https://cloud.githubusercontent.com/assets/2101743/4082694/f2a12f52-2ef3-11e4-8704-0646b60c4b5f.png)


#### On CasperJS
![CasperJS Demo](https://cloud.githubusercontent.com/assets/2101743/4082706/2a9b043c-2ef4-11e4-9632-dea51f8e4cdc.png)


Thank you!
@TooTallNate In addition, `process` global object is only available in node.js. so we can use this to determine running javascript environment.