hoa: add support for controllable-AP

* doc/spot.bib (perez.19.hoa): New entry.
* spot/parseaut/public.hh: Mention it.
* spot/parseaut/parseaut.yy, spot/parseaut/scanaut.ll: Learn to parse
the controllable-AP header.
* spot/twaalgos/hoa.cc: Print it.
* tests/core/ltlsynt.test, tests/core/parseaut.test,
tests/core/readsave.test, tests/python/_synthesis.ipynb,
tests/python/except.py, tests/python/games.ipynb,
tests/python/mealy.py, tests/python/synthesis.py: Adjust or augment
test cases.

NEWS

@@ -18,6 +18,10 @@ New in spot 2.10.2.dev  (not yet released)
   - sbacc() learned to take the "original-classes" property into
     account and preserve it.
 
+  - The HOA parser and printer learned to map the synthesis-outputs
+    property of Spot to the controllable-AP header for the Extended
+    HOA format used in SyntComp.   https://arxiv.org/abs/1912.05793
+
   Bugs fixed:
 
   - On automata where the absence of color is not rejecting