Add more tests for PQN.
Add Projecting trait for use in PQN and SPQ.
Make code more similar to original MATLAB version.
Make SPG more similar to original MATLAB implementation.
Use improvement over history as termination criterion in FirstOrderMinimizer.
Merge branch 'refactoring/pqn' of github.com:crealytics/breeze into crealytics-refactoring/pqn
add a gradient norm check to convergence criteria