Expose c-blosc's bitshuffle capability (fix #87)

[david-macmahon]

Shuffling is now a choice between no shuffling, byte shuffling, or bit
shuffling. This changes the type of the shuffle keyword in compress
from Bool to its supertype Integer. The previous "no shuffling"
(shuffle=false) and "byte shuffling" (shuffle=true) options map
cleanly onto the Integer assignments used by the Blosc library. These
constants have been added to the Blosc module:

• NOSHUFFLE (0) means do no shuffling (same as the old false)
• SHUFFLE (1) means do byte shuffling (same as the old true)
• BITSHUFFLE (1) means do bit shuffling (not previously supported)

The shuffled field in CompressionInfo has also been widened to
Integer to allow it to properly reflect all types of shuffling and the
compressor_info function properly decodes the flags to set the
shuffled field appropriately.

The tests have been updated to exercise all three shuffle modes.

[musm]

Hmm is this backward compatible? I.e. can we still pass in true and have it default to 1? Otherwise we might have to release a mitigating patch for backwards compatbility

[musm]

I've yanked the patch release, since this isn't backward compatible. I'll likely need to just make a new minor release and we need deprecation for the change.

[musm]

Instead of deprecation, we can also just re-add the existing method. It's kind of code smell, but would at least support the existing interface and add additional functionality without deprecation.

I don't have a strong preference either way, but thought I'd mention this too.

[david-macmahon]

I think it is backwards compatible. The tests for shuffle now test the following 5 value: NOSHUFFLE, SHUFFLE, BITSHUFFLE, true, false. Fortunately, NOSHUFFLE == 0 == false and SHUFFLE == 1 == true. Old code that used true/false should work seamlessly with the new code. The shuffle keyword was widened from Bool to Integer and Bool <: Integer.

[musm]

Perfect, when I took another look I think I saw Int and got worried, thankfully it's Integer