GDP helpers: slightly updated helper docs

[Graham Percival]

There have been a few minor changes to the GDP helper docs.  In
particular,
- we now recommend that lists in the @seealso section be separated
  with only one item per line.  The output looks the same, but the
  input is easier to add or remove items this way.
(you don't need to bother changing the current lists; I can do that
with a regex later on.  Just make new lists this way)
- advanced-tech.txt now has a "building the docs, even on
  windows" section.  This is by no means required; I don't mind
  fixing the occasional problem.  But if you'd like to see how the
  docs will look (kind-of), you could do this so you don't need to
  wait for X hours for me to commit your changes and rebuild the
  GDP server docs.

I'm actually using this latter method myself at the moment; it's
adequate for checking for compiling problems.

Cheers,
- Graham