Added GUI, execution times and Outputs are diff

GUI is simple, based and built using TkInter.
execution time is displayed.
Sobel is also added.
Output files are in .jpg formats.
Output files have names based on input files.

Thanks to Vishwanth for providing the canny code which helped me out in
y analysis project.
Added description of GUI usage

You must have the numpy, Scipy and, if used by the original method from shell, the PIL (Python Image Library)
Merge pull request #1 from prateekgarg/master

Added GUI and sample images with some results