this is a very stripped down and slightly modified re-implementation
of Ibrahim Sha'ath's keyfinder algorithm in java. everything not
vital for simply getting the key of some track has been omitted.

this tool expects raw 16 bit, signed, little endian, mono pcm data
that should have been downsampled to 5.512kHz sample rate. avconv
has proven useful to convert mp3 files to this format.

jkeyfinder needs java 8 and uses the JTransforms library.

see http://www.ibrahimshaath.co.uk/keyfinder/ for the original,
and https://github.com/ibsh/libKeyFinder for its code.