Fixes #2, basically black-and-white images have only 2 dimensions if loaded by OpenCV, thus, the concatenate with the main matrix fails due to shape assertion. Now, if len(img.shape) is 2 the image is converted to three dimensions.
Format the code.
create_imgs_matrix now ensures directory exists. Now both dif.compare_images('folder') and dif.compare_images('folder/') works.
len(img.shape)
is 2 the image is converted to three dimensions.