Added support for iterable datapoints

[pimterry]

This patch adds support for iterable datapoints, building on my previous work around all this stuff.

[dsaff]

Thanks. Two quick high-level notes:

1. We should probably upgrade some javadoc. It should especially note that iterable methods are invoked for every possible parameter, so expensive iterable methods are a bad idea.
2. This looks not to merge with HEAD

[pimterry]

Ah yes, sorry, my master it was slightly behind. I've now rebased the first commit over the other changes, and added documentation to @DataPoints to cover the basics of this.

[dsaff]

Looks good to me. Thanks! Can you add a release note?

[pimterry]

Done.