(Top): updated menu with new manual nodes

(Top): updated menu with new manual nodes
(The problem of spam): more ranting
(Anti-Spam Basics): "spammers are wise to [filtering on From:]"
(SpamAssassin): mention spam.el
(Hashcash): do not a sentence end proposition with
(Filtering Spam Using The Spam ELisp Package): more and better
explanation, took lots of information out into subsections
(Spam ELisp Package Sequence of Events)
(Spam ELisp Package Filtering of Incoming Mail)
(Spam ELisp Package Global Variables): new or updated content all
around
(Spam ELisp Package Configuration Examples): promised new
section, empty for now
(Blacklists and Whitelists, BBDB Whitelists)
(Gmane Spam Reporting, Bogofilter, spam-stat spam filtering)
(SpamOracle): mention that spam/ham processor variables are being
obsoleted
(Extending the Spam ELisp package): add some new documentation
for adding a new backend to spam.el