ignore the lat parameter of peer tag

ignore the lat parameter of peer tag

- It was redundent with the z coordinate of the peer.
- This changes the timings of the examples using the Vivaldi routing
- Also update and improve the documentation.
- doxygen don't quite like links to sections which names contain a
  html-like tag (as <peer>) and produce weird error messages in this case.
  Not much I can do here...