[fix] Naming of slides doesn't match those in slides-pdf/, will break links on course website

[jemus42]

Related to #22 in that it also requires changes to the website repository:

Some slides in slides-pdf which are linked from the website as well are named like this

slides-derivfree-1-coorddesc.pdf
slides-derivfree-2-nm.pdf
slides-derivfree-3-sa.pdf
slides-derivfree-4-multistart.pdf

But the corresponding files in slides/07-derivative-free have different names now for whichever reason:

slides-optim-derivative-free-1-coordinate-descent.tex
slides-optim-derivative-free-2-nelder-mead.tex
slides-optim-derivative-free-3-simulated-annealing.tex
slides-optim-derivative-free-4-multistart-optimization.tex

I don't have any opinion regarding which version is "correct", but they have to match such that the website links to the slides correctly.

[jemus42]

To resolve this, the contents of slides-pdf will have to be deleted and recompiled from the updated sources in slides/, and at that point the website will need to be updated with corresponding file path changes etc.