Moving to be OpenCV-free

We all know that OpenCV is a great tool for computer vision, but unfortunately it is also another dependency that needs to be installed and this could make some users unable to install and use the library (hey Windows users and non privileged users in networks). Because of this we are beginning the work to remove the use of OpenCV. We will read only pgm images, but you can still compile the library to use OpenCV and you'll be able to convert between Image and IplImage and to use OpenCV specific functions to open any image in libsmartreader.