Better length hoisting; fix bare "host" operator

* doc/Makefile: Remake .md files when pflua changes.

* doc/host-127.0.0.1.md: Regenerated, now with better length hoisting.

* src/pf/expand.lua (expand_host): Fix; should be "host src foo OR host
  dst foo", not AND.

* src/pf/optimize.lua (lhoist): Separately track the minimum packet
  length for an expression to evaluate as true or false.  This allows
  a more precise length computation.