Merge pull request #9 from vheun/master

updated to vuforia-sdk-ios-2-8-7
updated ofxQCAR examples with latest OF XCode changes.
making ofxQCAR more thread safe.
fixed up formatting of new extended tracking code

and replaced NSLog with ofLog.
updated README.
forgot about a simulator check.
added screenPointToMarkerPoint method.
fixed bug where target data sets were not being released correctly.
fixed small bug.
updated to work with OF latest master.
Merge with upstream