net spec draft repost

attached by request is a repost of the net spec draft that came out on
July 23, but including the images (its also in cvs under i2p/doc/specs/network_spec/).
 I'm revising the doc now fairly significantly, but this is still correct
for most things.

-jrandom
(the html here is exactly the same as http://article.gmane.org/gmane.comp.security.invisiblenet.iip.devel/292)