Updates the SDL library to the latest standard bugfix release

Engine/lib/sdl/docs/README.md

@@ -1,12 +1,6 @@
-Simple DirectMedia Layer {#mainpage}
-========================
+# Simple DirectMedia Layer
 
-                                  (SDL)
-
-                                Version 2.0
-
----
-http://www.libsdl.org/
+https://www.libsdl.org/
 
 Simple DirectMedia Layer is a cross-platform development library designed
 to provide low level access to audio, keyboard, mouse, joystick, and graphics
@@ -34,6 +28,7 @@ More documentation and FAQs are available online at [the wiki](http://wiki.libsd
 - [DirectFB](README-directfb.md)
 - [DynAPI](README-dynapi.md)
 - [Emscripten](README-emscripten.md)
+- [GDK](README-gdk.md)
 - [Gesture](README-gesture.md)
 - [Git](README-git.md)
 - [iOS](README-ios.md)
@@ -45,6 +40,7 @@ More documentation and FAQs are available online at [the wiki](http://wiki.libsd
 - [Supported Platforms](README-platforms.md)
 - [Porting information](README-porting.md)
 - [PSP](README-psp.md)
+- [PS2](README-ps2.md)
 - [Raspberry Pi](README-raspberrypi.md)
 - [Touch](README-touch.md)
 - [Versions](README-versions.md)