Implemented stream output for RGBAColor

In commit 950518f3 I changed the component type of RGBAColor from
16-bit to 8-bit integers. Unfortunately, in C++ 8-bit integers are
identical to characters, so this broke the writing of colors to
output streams.

src/gmenu2x.cpp

@@ -549,15 +549,8 @@ void GMenu2X::writeSkinConfig() {
 
 		int i;
 		for (i = 0; i < NUM_COLORS; ++i) {
-			inf << colorToString((enum color)i) << "=#";
-			inf.width(2); inf.fill('0');
-			inf << right << hex << skinConfColors[i].r;
-			inf.width(2); inf.fill('0');
-			inf << right << hex << skinConfColors[i].g;
-			inf.width(2); inf.fill('0');
-			inf << right << hex << skinConfColors[i].b;
-			inf.width(2); inf.fill('0');
-			inf << right << hex << skinConfColors[i].a << endl;
+			inf << colorToString((enum color)i) << "=#"
+			    << skinConfColors[i] << endl;
 		}
 
 		inf.close();

src/surface.cpp

@@ -27,7 +27,7 @@
 
 #include <algorithm>
 #include <cassert>
-#include <iostream>
+#include <iomanip>
 
 using namespace std;
 
@@ -44,6 +44,19 @@ RGBAColor RGBAColor::fromString(const string &strColor) {
 	};
 }
 
+ostream& operator<<(ostream& os, RGBAColor const& color) {
+	auto oldfill = os.fill('0');
+	auto oldflags = os.setf(ios::hex | ios::right,
+	                        ios::basefield | ios::adjustfield);
+	os << setw(2) << uint32_t(color.r)
+	   << setw(2) << uint32_t(color.g)
+	   << setw(2) << uint32_t(color.b)
+	   << setw(2) << uint32_t(color.a);
+	os.fill(oldfill);
+	os.setf(oldflags);
+	return os;
+}
+
 Surface *Surface::openOutputSurface(int width, int height, int bitsperpixel) {
 	SDL_ShowCursor(SDL_DISABLE);
 	SDL_Surface *raw = SDL_SetVideoMode(

src/surface.h

@@ -24,8 +24,10 @@
 #include "font.h"
 
 #include <SDL.h>
-#include <string>
+
 #include <cstdint>
+#include <ostream>
+#include <string>
 
 struct RGBAColor {
 	uint8_t r, g, b, a;
@@ -33,10 +35,11 @@ struct RGBAColor {
 	RGBAColor() : r(0), g(0), b(0), a(0) {}
 	RGBAColor(uint8_t r, uint8_t g, uint8_t b, uint8_t a = 255)
 		: r(r), g(g), b(b), a(a) {}
-	Uint32 pixelValue(SDL_PixelFormat *fmt) {
+	Uint32 pixelValue(SDL_PixelFormat *fmt) const {
 		return SDL_MapRGBA(fmt, r, g, b, a);
 	}
 };
+std::ostream& operator<<(std::ostream& os, RGBAColor const& color);
 
 /**
 	Wrapper around SDL_Surface