Add tests for examples from Nim in Action.

tests/niminaction/Chapter8/sdl/sdl_test.nim

@@ -0,0 +1,25 @@
+import os
+import sdl
+
+if sdl.init(INIT_VIDEO) == -1:
+  quit("Couldn't initialise SDL")
+
+var window: SdlWindowPtr
+var renderer: SdlRendererPtr
+if createWindowAndRenderer(640, 480, 0, window, renderer) == -1:
+  quit("Couldn't create a window or renderer")
+
+discard pollEvent(nil)
+renderer.setDrawColor 29, 64, 153, 255
+renderer.clear
+renderer.setDrawColor 255, 255, 255, 255
+var points = [
+  (260'i32, 320'i32),
+  (260'i32, 110'i32),
+  (360'i32, 320'i32),
+  (360'i32, 110'i32)
+]
+renderer.drawLines(addr points[0], points.len.cint)
+
+renderer.present
+sleep(5000)