twa: add support for prop_complete()

* spot/twa/twa.hh: Add support.  Make two constructors for prop_set in
order to diagnose constructions with 5 arguments.
* spot/parseaut/parseaut.yy: Adjust diagnostics for complete and
deterministic.
* spot/tl/exclusive.cc, spot/twa/twagraph.cc,
spot/twaalgos/alternation.cc, spot/twaalgos/complete.cc,
spot/twaalgos/complete.hh, spot/twaalgos/degen.cc,
spot/twaalgos/determinize.cc, spot/twaalgos/hoa.cc,
spot/twaalgos/isdet.cc, spot/twaalgos/mask.cc,
spot/twaalgos/minimize.cc, spot/twaalgos/product.cc,
spot/twaalgos/remfin.cc, spot/twaalgos/remprop.cc,
spot/twaalgos/sbacc.cc, spot/twaalgos/sccfilter.cc,
spot/twaalgos/simulation.cc, spot/twaalgos/strength.cc,
spot/twaalgos/stutter.cc, spot/twaalgos/totgba.cc,
tests/core/parseaut.test, tests/python/product.ipynb: Adjust.
* NEWS, doc/org/concepts.org, doc/org/hoa.org,
doc/org/tut21.org: Document it.

NEWS

@@ -10,6 +10,9 @@ New in spot 2.3.2.dev (not yet released)
   - spot::sum() and spot::sum_and() implements the union and the
     intersection of two automatons, respectively.
 
+  - twa objects have a new property: prop_complete().  This obviously
+    acts as a cache for the is_complete() function.
+
   Bug fixes:
 
   - In "lenient" mode the parser would fail to recover from