Initial commit of .NET port of FlatBuffers

Include C# codegen in flatc and .NET FlatBuffer access via the
FlatBufferBuilder class

Tested: on Windows.

Change-Id: If5228a8df60a10e0751b245c6c64530264ea2d8a

tests/MyGame/Example/Color.cs

@@ -0,0 +1,16 @@
+// automatically generated, do not modify
+
+namespace MyGame.Example
+{
+
+using FlatBuffers;
+
+public class Color
+{
+  public static byte Red = 1;
+  public static byte Green = 2;
+  public static byte Blue = 8;
+};
+
+
+}