128-bit key Murmur3 for 32-bit architectures.

Implemented 128-bit key Murmur3 with 128-bit keys for 32-bit
architectures. This was the first exercise of block buffering, which
revealed errors in that logic, now fixed. Further development made it so
that the buffering is not now exercised by the tests and remains
uncovered by tests.

Closes #18.