This enables generic code to reliably operate on the bits of an encoded
field element, by converting them to and from a known (little)
endianness.
The BitAnd and Shr bounds on PrimeField are now removed, as users can
perform these operations themselves as needed.
Building ff with the std feature flag was previously broken because it
required importing byteorder functionality behind the byteorder/std
feature flag. We don't use byteorder inside ff in no_std mode, so we can
just make it optional.
