[pstricks] [Web pages] New page for links and references

[Denis Girou]

  As the main Web page contained too many unordered references about PSTricks,
I create a new dedicated page for them, reorganize and update them:
http://tug.org/applications/PSTricks/Links.html

  Thanks to Rolf Niepraschk and Herbert Voss for their corrections in
the initial version.

D.G.