New code tries to guess a per-visitor IP address and uses
that (or its hash) to tell users apart.
This patch also adds a TAWASHI_WITH_IP_LOGGING cmake option
to enable or disable logging the IP address of your visitors
in various places (just one right now but don't assume things
to remain this way).
Also added a couple new CGI environment variables.
Env reads environment variables from the list it receives
from main(), so I can also pass it a forged list now
without needing extra classes with sometimes-virtual methods
or other cruft.
