Improve comments on Cong jumpahead.
Get rid of return value for C jumpahead() functions.
The equivalent C++ random API function discard() doesn't have a return value.
The Python random API jumpahead() function doesn't have a return value.
Get rid of return value for Python/Cython jumpahead() functions.
The Python random API jumpahead() function doesn't have a return value.
Add extra check for Python jumpahead() unit test.
Implement C Cong jumpahead() using 32-bit maths.
However, this uses a calculation of geometric series via recursion of O(log n) depth, which isn't ideal.