Merging Sorted Sequences

[CTMacUser]

This library adapts the C++ algorithm functions that take two sorted sequences and returns an also-sorted sequence that represents the set-difference, intersection, union, etc.. Instead of separate functions for each operation, the desired operation is selected by an enumeration value. (All the operations follow the same algorithm.) This includes an operation to do the general merge sort!

Checklist

• [x] I've added at least one test that validates that my change is working, if appropriate
• [x] I've followed the code style of the rest of the project
• [x] I've read the Contribution Guidelines
• [x] I've updated the documentation if necessary

[CTMacUser]

This is now obsolete from my next attempt at [#184].