Part 4a table of contents anchor link to second exercises does not work

[gwpantazes]

In Part 4a, there are two "Exercises" section, and thus two table of contents sidebar links to exercises. The table of contents sidebar link to the second exercises does not work, because the same ID is generated for both exercise sections in the document.

A possible solution: Could the markdown-to-HTML generator take into consideration repeat Headings and append a -2 onto the end of the second exercise section ID, making it distinct?

[Kaltsoon]

Thanks, we will look into this!