Detect lines in grayscale image using Hough Transform

Detection of lines (line segments) in a grayscale image using gradient-based Hough Transform.

Hough transform for line detection based on image's gradient field.

1. Operates on grayscale images, NOT B/W bitmaps.
2. NO loops involved in the implementation of Hough transform, which makes the operation fast.
3. Able to detect the two ends of line segments.