Move Windows-specific projects into separate solution.

src/Triangle.Rendering.GDI/ExtensionMethods.cs

@@ -0,0 +1,26 @@
+
+namespace TriangleNet.Rendering
+{
+    using System.Drawing;
+
+    internal static class ExtensionMethods
+    {
+        /// <summary>
+        /// Check if segment (a, b) intersects rectangle.
+        /// </summary>
+        public static bool Intersects(this RectangleF rect, PointF a, PointF b)
+        {
+            // TODO: implement intersection.
+            return rect.Contains(a) || rect.Contains(b);
+        }
+
+        /// <summary>
+        /// Check if triangle (a, b, c) intersects rectangle.
+        /// </summary>
+        public static bool Intersects(this RectangleF rect, PointF a, PointF b, PointF c)
+        {
+            // TODO: implement intersection.
+            return rect.Contains(a) || rect.Contains(b) || rect.Contains(c);
+        }
+    }
+}