Add a permalink functionality to section and diective-section in the generated doc.

This is convenient and consistent with httpd.a.o

Getting a link to a section or a directive is already possible from the TOC, but having it available directly in-place is, IMHO, much more useful.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1828588 13f79535-47bb-0310-9956-ffa450edef68