Is there an OS that doesn't support symlinks?  If so, should we delete the folder if it was copied (not symlinked)?  Of course, there's an argument to be made against a makefile's 'install' target to delete things.

Also, subsequent documentation builds will copy this regardless if it is out of date or not.  I notice a `copy_if_out_of_date` function on line 237.  I think I'd like that to be used here.