Add new glue code for writing native apps.

This factors out the boiler-plate code from the sample
app to a common glue code that can be used for everyone
writing this style of app: a dedicated app thread that
takes care of waiting for events and processing them.

As part of doing this, ALooper has a new facility to allow
registration of fds that cause ALooper_pollOnce() to return
the fd that has data, allowing the app to drive the loop
without callbacks.  Hopefully this makes some people feel better. :)

Also do some other cleanup of the ALooper API, plus some
actual documentation.

Change-Id: Ic53bd56bdf627e3ba28a3c093faa06a92be522b8

native/android/input.cpp

@@ -186,9 +186,9 @@ float AMotionEvent_getHistoricalSize(AInputEvent* motion_event, size_t pointer_i
 }
 
 void AInputQueue_attachLooper(AInputQueue* queue, ALooper* looper,
-        ALooper_callbackFunc callback, void* data) {
+        ALooper_callbackFunc* callback, void* data) {
     queue->setPollLoop(static_cast<android::PollLoop*>(looper));
-    ALooper_setCallback(looper, queue->getConsumer().getChannel()->getReceivePipeFd(),
+    ALooper_addFd(looper, queue->getConsumer().getChannel()->getReceivePipeFd(),
             POLLIN, callback, data);
 }