XPath normalize-space: small fix and docu added

- The function now also changes newlines to spaces.
- Added short description in the XPath documentation.
New XPath function sd:dummytext()

The new function returns more than 50 words of the dummy text
"Lorem ipsum" which can be used to test the layout without
real data.
Small documentation update

xml:base was just a test for an error message I’ve got - not needed