Fixes #2022, do not resume on Android when surfaceChanged

If the app is in landscape mode and the user presses the power button, a pause
is followed immediately by a surfaceChanged event because the lock screen
is shown in portrait mode. This triggers a "false" resume.
So, we just pause and resume following the onWindowFocusChanged events.

Also, wait for SDL_APP_WILLENTERBACKGROUND and SDL_APP_DIDENTERBACKGROUND before
blocking the event pump.

README.txt

@@ -0,0 +1,38 @@
+
+                         Simple DirectMedia Layer
+
+                                  (SDL)
+
+                                Version 2.0
+
+---
+http://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
+hardware via OpenGL and Direct3D. It is used by video playback software,
+emulators, and popular games including Valve's award winning catalog
+and many Humble Bundle games.
+
+SDL officially supports Windows, Mac OS X, Linux, iOS, and Android.
+Support for other platforms may be found in the source code.
+
+SDL is written in C, works natively with C++, and there are bindings 
+available for several other languages, including C# and Python.
+
+This library is distributed under the zlib license, which can be found
+in the file "COPYING.txt".
+
+The best way to learn how to use SDL is to check out the header files in
+the "include" subdirectory and the programs in the "test" subdirectory.
+The header files and test programs are well commented and always up to date.
+More documentation and FAQs are available online at:
+	http://wiki.libsdl.org/
+
+If you need help with the library, or just want to discuss SDL related
+issues, you can join the developers mailing list:
+	http://www.libsdl.org/mailing-list.php
+
+Enjoy!
+	Sam Lantinga				(slouken@libsdl.org)
+