Mistake in quickref.html about formatting the exercise section

[aless80]

quickref.html shows under the "Section Types" paragraph that exercises can be surrounded by 7 = characters. When I try this I get a compilation error (not shown).

The documentation is probably wrong/obsolete on this point. In fact, according to manual.html Exercises, Problems, Projects, and Examples are subsections and should be surrounded by 5 = characters. Also book.pdf defines exercises as a subsections.

[aless80]

Addressed in doconce/dodonce, issue 23