reworked Makefile to compile against OpenCV 3.0 (fixes #175)
reworked Makefile to compile against OpenCV 3.0 (fixes #175)

- some refactoring
- handle new MxArray files (and future ones) added when moved to OpenCV 3.0
- add new target to compile with opencv_contrib support
- fix the use of VPATH which is designed to find sources, not targets
- test for OpenCV with pkg-config, and issue an error if it fails
- add help descriptions

bearpaw/mexopencv,fengzhyuan/mexopencv,fengzhyuan/mexopencv,CVML/mexopencv,nanit/mexopencv,nanit/mexopencv,CVML/mexopencv,bearpaw/mexopencv