These correspond to the first three blocks of table 1 in S. Sickert,
J. Esparza, S. Jaax, and J. Křetínský: Limit-Deterministic Büchi
Automata for Linear Temporal Logic. CAV'16. LNCS 9780.
For #353.
* spot/gen/formulas.cc, spot/gen/formulas.hh, bin/genltl.cc: Implement
the new families.
* tests/core/genltl.test: Test it.
* bin/man/genltl.x, NEWS: Document it.