Add tests for examples from Nim in Action.

tests/niminaction/Chapter8/sfml/sfml.nim

@@ -0,0 +1,26 @@
+{.passL: "-lsfml-graphics -lsfml-system -lsfml-window".}
+
+type
+  VideoMode* {.importcpp: "sf::VideoMode".} = object
+  RenderWindowObj {.importcpp: "sf::RenderWindow".} = object
+  RenderWindow* = ptr RenderWindowObj
+  Color* {.importcpp: "sf::Color".} = object
+  Event* {.importcpp: "sf::Event".} = object
+
+{.push cdecl, header: "<SFML/Graphics.hpp>".}
+
+proc videoMode*(modeWidth, modeHeight: cuint, modeBitsPerPixel: cuint = 32): VideoMode
+    {.importcpp: "sf::VideoMode(@)", constructor.}
+
+proc newRenderWindow*(mode: VideoMode, title: cstring): RenderWindow
+    {.importcpp: "new sf::RenderWindow(@)", constructor.}
+
+proc pollEvent*(window: RenderWindow, event: var Event): bool
+    {.importcpp: "#.pollEvent(@)".}
+
+proc newColor*(red, green, blue, alpha: uint8): Color
+    {.importcpp: "sf::Color(@)", constructor.}
+
+proc clear*(window: RenderWindow, color: Color) {.importcpp: "#.clear(@)".}
+
+proc display*(window: RenderWindow) {.importcpp: "#.display()".}