The basic idea of product quantization is 10 years old now and there are many examples out there [0][1][2][etc]. This looks like a high quality library though.

[0] https://github.com/yahoo/lopq

[1] https://github.com/cgtuebingen/Product-Quantization-Tree

[2] https://github.com/technicolor-research/pq-fast-scan

[3] https://github.com/matsui528/rii