Even more titles

[Tanaquil18]

Titles for Chapters D, E, and LT. I used more standard capitalization rules, thinking of titles appearing in the book, instead of just as a note to instructors using Runestone.

[rbeezer]

Also merged locally - once I make all my changes public, then it'll be recorded here, so leave these open for now.

git education - see how there are 5 commits here? Two from #102, plus three new ones? Best practice would have been to start a new branch for the later three on #103. Or you could have pushed the old branch to #102 and updated it to have all five before I got to it (less ideal).

No matter, git was "smart" enough to see the duplication (which had not noticed until I saw git noticed!).

Thanks very much, @Tanaquil18, it'll be nice having these.