Address huf / piz performance regressions (#1868)

* Enable fast huf for os/x, optimize routines

Signed-off-by: Kimball Thurston <[email protected]>

* Apply some minor optimizations to piz decode

Signed-off-by: Kimball Thurston <[email protected]>

* disable alias tag for msvc

It appears MSVC does not handle the restrict keyword properly

Signed-off-by: Kimball Thurston <[email protected]>

* Replicate comment denoting issue w/ msvc

Signed-off-by: Kimball Thurston <[email protected]>

* Remove overzealous memory optimization

It is more efficient to store the code length and symbol in the one
table, but appears measurably slower. Remove that.

Further, do not constantly refill the bit buffer during huf fast decode,
that slows down the decoding

Signed-off-by: Kimball Thurston <[email protected]>

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Signed-off-by: Kimball Thurston <[email protected]>