Tzz/redmine 2081 data facilities

These are implementations of several functions from Redmine#2081:

* `every`, `none`, and `some`: test a slist for matches and return a class expression if every/none/some of the elements match.  Quits early when possible.

* `nth` and `sublist`: extract the slist elements at a specified offset or between offsets

* `uniq`: get only the unique elements of an slist

* `filter`: filter an slist by regex or exact match, getting up to