Reorganize types

- Move into types folder
- Group types based on usage

Raylib-cs/types/RenderTexture2D.cs

@@ -0,0 +1,26 @@
+using System.Runtime.InteropServices;
+
+namespace Raylib_cs
+{
+    /// <summary>
+    /// RenderTexture2D type, for texture rendering
+    /// </summary>
+    [StructLayout(LayoutKind.Sequential)]
+    public struct RenderTexture2D
+    {
+        /// <summary>
+        /// OpenGL Framebuffer Object (FBO) id
+        /// </summary>
+        public uint id;
+
+        /// <summary>
+        ///  Color buffer attachment texture
+        /// </summary>
+        public Texture2D texture;
+
+        /// <summary>
+        /// Depth buffer attachment texture
+        /// </summary>
+        public Texture2D depth;
+    }
+}