restore significant whitespace to CDATA sections

I have found this makes the documentation more useable.

This minor edit of documentation restores formatting that was in [this 145dfb12 version](https://raw.githubusercontent.com/saxonica/Saxon-CE/145dfb124fe9e7768be82f7266642b65cff94a39/user-doc/doc/api.xml) of the file and contains no code written by me, so I ask that you waive the contributor agreement.  I am an exempt-from-fair-labor-standards employee of the regents of the university of california, so I would probably have to run any contributor agreement though contracts and grants or something like that.