Added in decorrelated cross product with a common suffix.
Change parameter order for decorrelated cross product - will make subsequent work a little easier.
Add in extra unit tests to deal with cross products using common suffices after diagnosing a bug in the decorrelated cross product via a higher-level test. The one for the decorrelated cross product is expected to fail in this commit.
Decorrelated cross product implementation now passes both unit tests introduced in the previous commit.
Introduced the use of the decorrelated cross product into the 'Node' implementation, and removed the original randomisation hacks in 'Node'. Ironically, this doesn't randomise the use-case for large amounts of interleaving - because these result in long cross product suffices, which are deliberately *not* decorrelated. I'll sor thtis out in the next commit.
Now mixing up test variable combinations from interleaves very nicely - looking good with the massive interleaving test.