cwida/PDX: v0.3 - 30x faster index construction with SuperKMeans

Faster indexing with SuperKMeans We replaced FAISS with SuperKMeans for constructing our partition index. Expect 10-30x faster construction. With SuperKMeans, you can index 10M vectors in 1 minute with a single CPU. Other Changes PDX is now a more mature library with a nicer API (documentation coming soon) Eliminated the dependency on FAISS C++ methods for PDXification in 32-bit and 8-bit. Several bugs and memory leak fixes. Support for U8 in AVX2. Adding unit tests and code formatting. Adding CI suite