Create greyscale_entropy.m

Takes an amount of images (expects files to be images) and separates gray scale images into 4 sub-images. Returns the entropy value for the original one and for the sub-images generated during runtime.

![Lena Image](http://i.imgur.com/5pfaizv.jpg)


![Lena Sub-Images](http://i.imgur.com/5KGEJGc.jpg)