VS2012 static lib project method

Offers an option for VS users to include ofxCv (with opencv) as a static lib project within their solution.
I've made notes in the readme also regarding how to set this up and why you might want to use this method.

I recently did the same for ofxTimeline:
https://github.com/YCAMInterlab/ofxTimeline/tree/master/ofxTimelineLib