Improved imfindcircles method

This is a very simple modification of the "imfindcircles" method, that uses the "Canny" algorithm for edge detection

The matlab "imfindcircles" method is excellent at detecting circular objects in images. However, the first step in the algorithm is to detect edges, and the currect method for edge detection (convolution with the sobel operator and thresholding), is not optimal.

This code modifies the function "chaccum", to utilize "Canny" edge detection. With this modification, the algorithm was found to be substantially more robust in detecting the true circles and far fewer spurious circles. The new code was used to analyze a batch of fluorescence microscopy images and showed better overall results compared to the built-in function.

The only function that was actually changed was "chaccum". All of the rest were simply copied from the built-in method.