Added bitmap size and clipping to rasterize.js

Added support for defining window/viewport size and eventual clipping to bitmap rasterization similar to how it is used with paper output.
Pass modifier to mouse events for click/dblclick

A fix for the issue described here:

https://github.com/ariya/phantomjs/issues/11867
Merge pull request #11866 from bmarkovic/patch-1

Added bitmap size and clipping to rasterize.js
Update some grammar on the README.md

Replaces the "a, b, c, d" with the more grammatically correct "a, b, c, and d"
Adding tests for #11867

This tests mousedown, mouseup, click, and doubleclick for clicks with
modifier events. The mousedown/mouseup tests pass in 1.9.2, the
click/doubleclick do not. All pass with a build from this branch.
Merge pull request #11868 from bradleyboy/click-modifier-fix

Pass modifier to mouse events for click/dblclick
Merge remote-tracking branch 'upstream/master'
Merge branch 'master' of github.com:neraliu/phantomjs