Function render

Render a rectangle of the Mandelbrot set into a buffer of pixels. The `bounds` argument gives the width and height of the buffer `pixels`, which holds one grayscale pixel per byte. The `upper_left` and `lower_right` arguments specify points on the complex plane corresponding to the upper- left and lower-right corners of the pixel buffer.

(pixels: &mut [u8],
          bounds: (usize, usize),
          upper_left: Complex<f64>,
          lower_right: Complex<f64>)