Merge pull request #396 from RickEyre/stringlist-pop

Add stringlist_pop func and tests.
Add node list struct.

The node list struct simplifies working with lists of nodes and will
allow us to build more complex things with node lists in the future.
It seemed prudent to make this change now as the lang tag is
introducing a number of complexities which need us to refactor code.
Due to this it is a good time to make this change.