Add more optimization routines

[anthonyclays]

The only optimization procedure currently implemented is the golden section method. Optimization of functions with more than one variable (most notable Rosenbrock's function) is impossible without other methods.

Some initial suggestions:

• nelder-mead
• BFGS

For a well-written, high-level, fast and clear example of those (and other) routines, I highly recommend checking out Optim.jl.