Add an algorithm to split an automaton in several automata.

* bench/scc-stats: New directory.  Contains input files and test
program for computing statistics.
* bench/split-product: New directory.  Contains test program for
synchronised product on splitted automata.
* bench/split-product/models: New directory.  Contains Promela
files and LTL formulae that should be verified by the models.
* src/tgba/tgbafromfile.cc, src/tgba/tgbafromfile.hh:
New files.  Small class to avoid long initializations with numerous
constants when translating to TGBA many LTL formulae from a
given file.
* src/tgbaalgos/cutscc.cc, src/tgbaalgos/cutscc.hh:
New file.  From a single automaton, create, at most,
X sub automata.
* src/tgbaalgos/scc.cc, src/tgbaalgos/scc.hh:
Adjust to compute self-loops count.