[NEW] Matching problems

[Rob Beezer]

Recently, we made a cosmetic change to interactive matching exercises to use the
term "cardsort" for some of the markup.

That was, in part, preparation for a "more general" matching question, where any
#premise can be matched to any #response, and vice versa. These are available
now. The Runestone Sevices implementation (online) allows the reader to create
a bipartite graph to indicate the matchings.

This was a collaboration with Brad @ Runestone. Thanks, Brad!

Exercise 5.: Matching Problem, Playing Cards
https://pretextbook.org/examples/sample-book/noparts/html/matching-exercises.html#matching-playing-cards

Exercise 6.: Matching Problem, Popular Music History
https://pretextbook.org/examples/sample-book/noparts/html/matching-exercises.html#matching-music-history

As usual, questions or reports can go to pretext-support or pretext-dev. And
there may be some fine-tuning necessary, so do not hesitate to comment.

Rob