Make adjustments to fix tbloom for python 3

Make adjustments to fix tbloom for python 3

Make the changes needed to get the tbloom tests passing with python 3.
Change the C helper argument conversions to types that work with each
version (there didn't appear to be a good, shared common format string
type).  Switch to a Py_buffer in some places because python 3 didn't
appear to have a conversion that would convert all the binary
inputs (buffer/memoryview/...) to a plain C byte array the way python
2 can.

Change all the other typical things, i.e. byte paths, '' to b'', and
// for integral division, etc.

With this, tbloom should pass with both python major versions (python
3 version tested was python 3.7.5).

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Tested-by: Rob Browning <rlb@defaultvalue.org>