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.

doc/spot.bib

@@ -726,6 +726,15 @@
   doi		= {10.1007/978-3-540-73370-6_17}
 }
 
+@Misc{		  perez.19.hoa,
+  author	= {Guillermo A. P{\'{e}}rez},
+  title		= {The Extended {HOA} Format for Synthesis},
+  howpublished	= {ArXiv},
+  month		= {dec},
+  year		= {2019},
+  url		= {http://arxiv.org/abs/1912.05793}
+}
+
 @InProceedings{	  piterman.06.vmcai,
   author	= {Nir Piterman and Amir Pnueli and Yaniv Sa'ar},
   editor	= {E. Allen Emerson and Kedar S. Namjoshi"},