Closing keyboard after entering last digit shouldn't be automatic

[jlbruno]

Currently, after you enter the last digit in your pin number, the keyboard closes automatically:
https://github.com/PixelMEDIA/android-pin-number/blob/master/src/com/pixelmedia/androidpinnumber/PinNumberTextWatcher.java#L30

This behavior should likely be determined by the app using the library, not the library. We should look into whether this can be a toggled option, or maybe a callback or some sort.