Do we want to introduce unit tests as standard?
   Clean up unit tests in inst/unittests and make sure that they work

Look for ?? anywhere

Change output of optimr to return extra information in attributes
   - gradient
   - hessian
   - counts of these
  NOT included at 180710. 
  It will require new code in EVERY optimizer, but might be worth it.
  Or add an optimra() function to develop this.




