use a bibtex file to collect all references in Doxygen

* doc/tl/tl.bib: Move ...
* doc/spot.bib: ... here, and augment it with all references that
appeared verbatim in Doxygen comments.
* doc/Makefile.am, doc/tl/Makefile.am
doc/tl/tl.tex: Adjust for the move.
* doc/Doxyfile.in: Point to spot.bib.
* spot/gen/automata.hh, spot/gen/formulas.hh, spot/misc/game.hh,
spot/misc/minato.hh spot/taalgos/emptinessta.hh,
spot/taalgos/minimize.hh, spot/taalgos/tgba2ta.hh, spot/tl/formula.hh,
spot/tl/remove_x.hh, spot/tl/simplify.hh, spot/tl/snf.hh,
spot/twaalgos/cobuchi.hh, spot/twaalgos/cycles.hh,
spot/twaalgos/dualize.hh, spot/twaalgos/gtec/gtec.hh,
spot/twaalgos/gv04.hh, spot/twaalgos/ltl2taa.hh,
spot/twaalgos/ltl2tgba_fm.hh, spot/twaalgos/magic.hh,
spot/twaalgos/minimize.hh, spot/twaalgos/parity.hh,
spot/twaalgos/powerset.hh, spot/twaalgos/randomgraph.hh,
spot/twaalgos/se05.hh, spot/twaalgos/simulation.hh,
spot/twaalgos/strength.hh, spot/twaalgos/stutter.hh,
spot/twaalgos/tau03.hh, spot/twaalgos/totgba.hh,
spot/twaalgos/toweak.hh: Use \cite instead of a verbatim bibtex entry.

spot/twaalgos/parity.hh

@@ -140,17 +140,7 @@ namespace spot
   ///
   /// This implements an algorithm derived from the following article,
   /// but generalized to all types of parity acceptance.
-  /** \verbatim
-      @Article{carton.99.ita,
-      author       = {Olivier Carton and Ram{\'o}n Maceiras},
-      title        = {Computing the {R}abin index of a parity automaton},
-      journal      = {Informatique théorique et applications},
-      year         = {1999},
-      volume       = {33},
-      number       = {6},
-      pages        = {495--505}
-      }
-      \endverbatim */
+  /// \cite carton.99.ita
   ///
   /// The kind of parity (min/max) is preserved, but the style
   /// (odd/even) may be altered to reduce the number of colors used.