Canny edge detection 2D

Canny edge detection for 2D images

This canny edge detection function was based on GAGAN's original implemented. Computation speed was improved by about 100 times.

1. A different way of non-maxima suppression, completely in matrix format, avoiding if-then statements. This step is about 50 faster
2. A different way of connectivity analysis using imfill. This step is about 400 times faster.

----

Original description from GAGAN's original submission:
------------------------------------------------------
The Canny Edge detection method relies on various steps:
1. Convolution with Gaussian.
2. Estimation of Gradient Vector.
3. Non Maxima Suppression.
4. Thresholding and Connectivity Analysis.