These are safety, guarantee, obligation, persistence, and recurrence.

* src/ltlast/formula.hh, src/ltlast/formula.cc: Declare a bit for
each of these classes.
* src/ltlast/atomic_prop.cc, src/ltlast/constant.cc,
src/ltlast/automatop.cc, src/ltlast/binop.cc, src/ltlast/bunop.cc,
src/ltlast/unop.cc: Update these bits.
* src/ltltest/kind.test: Update tests and add more.