gradient_tolerance not needed in test suite any more.
Only use step length heuristic for L-BFGS once.
spii::wall_time in DLL on Windows.
Linear programming example updated.
More economical temporar hessian storage.
LBFGS: Do not check exit condition the first iteration.
Fix warning in linear programming.
Add denoising example.

Same objective functions as in Ceres Solver.