Add Ben's suggestions of methods for a single SourceID: C'tor, MatchOnly(), Add(), Remove().

Also take the opprtunity to refactor the class to make more use of self messaging.
Added Merkle-Damgaard version of MurmurHash2 for use in hashing BankSelections.  Verified hash operation (i.e. no bugs itroduced by me!)  by comparisons with one-shot MurmurHash2 function. Both versions currently available.

Verification~  the two versions should be (& are) equivalent if:
* one-shot version does not XOR(seed, length) at start.
* M-D version does not mix the tail and size at the end.

Files will be cleaned up in later commits, now that implementaion is checked.
Convert MurmurHash2 bit scramblers to MurmurHash3 versions.
Add in any tail into the hash when it is being ended.
REmove debug statements, tidy up.