API description

Printer API

 There are three layers of printer API, the lower layer is C, the device provid C interface, and the third app to write their own JNI source by calling the C interface.
 The middle layer is JNI interface, wizarPOS write JNI source and generate the device so files, so the third app just use the JNIInterface to finish the calling.
 The upper layer is Java interface, wizarPOS provide Java interface for the third app, the third app only need to import the .aar pakcage to their libs.