Update CMakeLists.txt meta-information.
Fix the initialization of lastState

There is however an error remaining (boost::optional data is
destroyed at some point, resulting in the impossibility to get
the last state of a SolverError. Investigation is in progress).
Add a test for the result value of a SolverError
Update documentation for DummySolverLastState.
Merge pull request #4 from bchretien/master

Fix master branch and add a unit test with lastState
Update authors information.
Add CONTRIBUTING.md.
fixed NTimesDerivativeFunction::derivative assertion.
method does not access correct version of the multiple
"static const int derivabilityOrder" which exist in the
inheritance tree.
Merge pull request #5 from awernerdlr/fix_derivability_order

fixed NTimesDerivativeFunction::derivative assertion.
Aethestic changes.
Provide a way to visualize jacobian structures with Gnuplot.