* spot/gen/formulas.hh, spot/gen/formulas.cc (genltl): Rename as...
(ltl_pattern): This.
(ltl_pattern_max): New function.
* bin/genltl.cc: Adjust names, and simplify using ltl_pattern_max().
* python/spot/gen.i (ltl_patterns): New function.
* tests/python/gen.py: Test it.
* tests/python/gen.ipynb: New file to document the spot.gen package.
* tests/Makefile.am, doc/org/tut.org: Add gen.ipynb.
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.
