Add support for `zoomFactor`

Note that I also fixed windowX and windowY parameters while at it. I was
using the wrong property names at webshot.
Merge pull request #3 from bebraw/zoomFactor

Add support for `zoomFactor`
Merge branch 'master' of github.com:Codegyre/phantomshot

Conflicts:
	capture.js
	package.json
	rasterize.js
	serve.js
nmp 6