Non-linear least squares added

Add wrapper for (just unbounded so far) non-linear least squares
functions.
Change name

Change name
Add non-linear least squares MKL wrapper

Add non-linear least squares MKL wrapper and suggested form for
Optimization routines.
Add options for NonLinearLeastSquaresMinimizer.

Add options for NonLinearLeastSquaresMinimizer.
NonLinearLeastSquaresMinimizer change API
Very preliminary Brent and Powell minimizations.
Cleaning up Powell and Brent minimizers.
Add more comments.
More tidying up of minimizers.
Reduce tolerance.