This introduces a couple of new datastructure-related utility functions

that will be used in some upcoming changes.
filter_dup_list_items() takes a list of items and filters out any

duplicates, ensuring that there is one of each instance in the list.

This is similar to passing a list into set(), but preserves the order.
merge_dicts() merges two dictionaries together. Its approach is

simplistic but sufficient for our needs. Keys present only in the source

dictionary are placed in the destination. Lists are concatenated.

Dictionaries are recursively merged. Anything else triggers an error.
Unit tests and doc generation were added for these new functions.

Unit tests pass.
Tested these in upcoming changes.