Fixes#254.
* spot/gen/formulas.cc, spot/gen/formulas.hh: New files.
* spot/gen/Makefile.am: Add them.
* spot/Makefile.am: Fix build order.
* bin/genltl.cc: Move most code to the above files and adjust.
* bin/Makefile.am: Link genltl with libspotgen.
* doc/org/arch.tex: Adjust picture to show that genltl uses
libspotgen.
* python/spot/gen.i: Include formulas.hh.
* tests/python/gen.py: Make sure genltl() and ltl_pattern_name()
can be called.
Similarly to genltl that generates LTL formulas for various classes that
appear in the literature, genaut generates automata.
* NEWS: Mention the modification.
* bin/Makefile.am: Build the new binary.
* bin/genaut.cc: The new binary itself.
