Updated website w/ book info

[Philipp K. J. <ja...@ie...>]

Just as a heads-up to everyone: Now that the book
is available in print, I have updated the information
on the gnuplot.info homepage accordingly, and also
put a link on the documentation page.

The old versions of the index.html and the documentation.html
pages are still there, as "_29Aug2009.html", so that we
can revert if needed.

Best,

		Ph.