ProGuard

ProGuard is a tool that shrinks, optimizes and obfuscates code, and is commonly used in Android development to reduce the size of .apk.

Thanks to @black-snow for providing these settings:

-keep class com.drew.** {*;}
-keep interface com.drew.** {*;}
-keep enum com.drew.** {*;}

Please be aware that the above rules may not be ideal but they should hold your release apk together. Feel free to contribute an optimized ruleset.