Add tasks for all the new languages

Task/Grayscale-image/Sidef/grayscale-image.sidef

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+require('Image::Imlib2')
+
+func tograyscale(img) {
+    var (width, height) = (img.width, img.height)
+    var gimg = %s'Image::Imlib2'.new(width, height)
+    for y,x in (^height ~X ^width) {
+        var (r, g, b) = img.query_pixel(x, y)
+        var gray = int(0.2126*r + 0.7152*g + 0.0722*b)
+        gimg.set_color(gray, gray, gray, 255)
+        gimg.draw_point(x, y)
+    }
+    return gimg
+}
+
+var (input='input.png', output='output.png') = ARGV...
+var image = %s'Image::Imlib2'.load(input)
+var gscale = tograyscale(image)
+gscale.set_quality(80)
+gscale.save(output)