[BREAKING] ae.utils.graphics: Constness fixes

Make opIndex[x, y] callable with const objects.

Changes required:

- If you have a view using DirectView and implementing the scanline
  method, ensure it is callable with a const this.

Author: CyberShadow

utils/graphics/gdi.d

@@ -55,7 +55,7 @@ struct GDICanvas(COLOR)
 	int w, h;
 	COLOR* pixels;
 
-	COLOR[] scanline(int y)
+	inout(COLOR)[] scanline(int y) inout
 	{
 		assert(y>=0 && y<h);
 		return pixels[w*y..w*(y+1)];

utils/graphics/image.d

@@ -32,7 +32,7 @@ struct ImageRef(COLOR)
 	COLOR* pixels;
 
 	/// Returns an array for the pixels at row y.
-	COLOR[] scanline(int y)
+	inout(COLOR)[] scanline(int y) inout
 	{
 		assert(y>=0 && y<h, "Scanline out-of-bounds");
 		assert(pitch, "Pitch not set");
@@ -75,7 +75,7 @@ struct Image(COLOR)
 	COLOR[] pixels;
 
 	/// Returns an array for the pixels at row y.
-	COLOR[] scanline(int y)
+	inout(COLOR)[] scanline(int y) inout
 	{
 		assert(y>=0 && y<h, "Scanline out-of-bounds");
 		auto start = w*y;

utils/graphics/view.d

@@ -44,10 +44,11 @@ enum isDirectView(T) =
 /// existing direct view primitives.
 mixin template DirectView()
 {
-	alias COLOR = typeof(scanline(0)[0]);
+	import std.traits : Unqual;
+	alias COLOR = Unqual!(typeof(scanline(0)[0]));
 
 	/// Implements the view[x, y] operator.
-	ref COLOR opIndex(int x, int y)
+	ref inout(COLOR) opIndex(int x, int y) inout
 	{
 		return scanline(y)[x];
 	}