Useful tools

With a quick overview of PaintView, I found that it's a powerful canvas. However, It's a little wired that why a `View` needs javax encryption API? 

I'm sure that there's no need to call `Bitmap.recycle()` anymore since Android 4.0, because Android 4.0 moved the Bitmap from native heap to dalvik heap. Once there is no strong reference to a Bitmap, it will be garbage collected.
