On earlier pythons we don't have the ability to set the size of
SHAKE-256 output, so we need to use our own implementation.

coveralls complains about branches that haven't been executed on
all environments, but that's expected if the branch is environment
specific, so skip those

as extra_entropy can be large, and different type than outputs
from either bits2octets or number_to_string, do not concatenate
them but rather push them to the hmac one by one

don't use six.b(), not needed on py2.6

simplify the chained comparison and remove unneeded else after return
in rfc5979.generate_k

this is repeating the s[x] three times for every element extracted,
use a function for that

also decreases number of tests needed for condition coverage

make the bytearray work on pythohn2.6
make multi-byte array.array objects work on all versions