How to transform the docs to html:
call
$ xmlto html doc.xml
from within the reference directory

cross-referecing
----------------
there is a small ruby script which collects all id="" thingies from the xml files in xml and creates links around the symbols found in files.
exceptions:
- there is already a link around a symbol.
- its part of a function: cairo_translate !=> <link>cairo_t</link>ranslate