Convenience functions

Among other things, add `stack-core-filter-data' to create subfilters within elisp itself.

Also move test suite to its own directory and create a means to load that data quickly.
Well I have to say… I don't know how to do this without recursion, really. https://gist.github.com/vermiculus/685022fdf1347ec8d097 is an attempt, but I'm going to ask on SO to see if anyone there can help me out.