Code overhaul

Manage library_locations as a double-null terminated string.
Enable pure-native usage: Initialize library_locations with LD_LIBRARY_PATH if JNI initializer is not called.
Enable usage as an Android library.
Create 'test', Android JUnit-based test project.
Move native testing code to into JUnit test project; ndk-build NATIVE_TEST=1 (in 'test' project) to build it.