This patch increases the reliability of the solver.

• Fixed bug when the solver could not recover from divergence and could not redo the last time step correctly
• Type dual_type deprecated but still supported, added state_value instead as it is clearer
• Added recover_from_linsolver_failure solver option (true by default). Now the solver will try to recover from the linear solver failure (e.g., on the matrix decomposition step) by rolling back and decreasing the time step.

Documentation: dae-cpp.github.io