[racket-dev] code coverage coloring

It would be nice if I could turn on coverage highlighting from code in
my language's run-time configuration, without the user having to
(remember to) click anything at all.  My #lang already sets things
like pconvert options (which too they could have set by clicking,
except I did it for them).  I'd like it to be able to set this, too,
from the #lang rather than requiring another plugin.

Shriram