Create colours module with colour definitions

examples/hough.rs

@@ -2,20 +2,13 @@ mod common;
 
 use ccvl::*;
 
-const LINE: image::SRGBA = image::SRGBA {
-    r: 1.0,
-    g: 0.0,
-    b: 0.0,
-    a: 1.0,
-};
-
 fn main() -> std::process::ExitCode {
     common::process_image(|mut img| {
         let greyscale = img.map(|p| image::Luminance::from(p));
         let edges = filter::canny(greyscale);
         for line in hough::lines(10.0, edges) {
 			let ((x0, y0), (x1, y1)) = endpoints(line, img.extent);
-			draw::line(x0, y0, x1, y1, &mut img, LINE);
+			draw::line(x0, y0, x1, y1, &mut img, colours::RED);
         }
         img
     })