Add PhysicsEffects to Extras. The build is only tested on Windows and Android.

The Android/NEON optimized version of Physics Effects is thanks to Graham Rhodes and Anthony Hamilton, See Issue 587

Extras/PhysicsEffects/README_Android.txt

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+This file set contains new files, and changes to existing files, that will enable PhysicsEffects
+and several sample apps to be built and run on Android devices. The Android projects are
+a mix of Java and C++ code. The code has been tested using Android NDK r5c. Build files
+are provided for the NDK and ANT. Here are some instructions on how
+to update the baseline PhysicsEffects branch of Bullet to support Android using the provided
+files:
+
+1. For Windows platforms, download and install Cygwin (if it is not already installed)
+2. Download and install the Android SDK.
+3. Download and install the Android NDK. (The files provided have been tested with NDK r5c.)
+
+4. Set up these new environment variables:
+
+    BULLET_PFX_ROOT_CYGWIN = path to your PhysicsEffects folder, for example:
+    BULLET_PFX_ROOT_CYGWIN=/cygdrive/d/tools/Bullet/branches/PhysicsEffects
+
+    CYGWIN_ROOT = path to where Cygwin is installed (Windows-style path)
+    ANDROID_NDK_ROOT = path to where the Android NDK is installed
+
+5. Open a Cygwin console. Browse to the PhysicsEffects/project/Android
+      folder. Then, for each package, starting with PfxLibrary, go into the
+      package folder and run the ndk-build command. For example:
+
+      /PhysicsEffects/project/Android/PfxLibrary> /cygwin/d/tools/android-ndk-r5c/ndk-build
+
+      Build every package using ndk-build.
+
+      (It is possible to configure Eclipse to use ndk-build, but that is somewhat
+      tedious to do.)
+
+6. For each application package (PfxApp*) after running ndk-build use
+	    ant compile
+	    ant debug
+
+	 If your Android device is connected and setup, you can also run the app using
+	    ant install
+
+7. If you run the app, you can interact with the touch interface:
+
+      - Tap the screen to change scenes
+      - Pinch the screen to zoom in/out
+      - Drag the screen to rotate the camera