Rename 'ok()' to 'isFine()' and add docstring.

That satisfies pylint(1).
Remove unused import.
Rename 'HMACKey' to 'hmacKey'.

That satisfies pylint(1) and is easier to read.
Move 'MAX_BINS' and 'MIN_BINS' to const.py.
Rename 'b' to '_' since it is unused.
Rename 'p' to 'prob'.