JS decoder supporting "advanced" encodings

[springmeyer]

The JS decoder does not yet support the FastPFor or FSST encodings. These compress better and are faster to decode. So if the JS decoder can add support for these we should be able to see significant improvements to efficiency.

TODO:

• Add support for these encodings
• Regenerate the test fixtures in ./test/expected to use the encodings
• Ensure the JS decoder is robust
• Re-run benchmarks comparing the improvements against the default encodings currently used (mainly RLE and Varint)