MINOR: deinit: fix memory leak

deinit() did not free the conf.file member of server objects.
DOC: clearly state that the "show sess" output format is not fixed

It requires to look at the code (src/dumpstats.c) since the format may
change at any moment.
DOC: missing track-sc* in http-request rules

track-sc is well defined in http-request rules, but not listed in
option list.
This patch fix this miss.