Replace hardcoded images with figures produce during documentation built

[navidcy]

Instead of adding png files in the docs, like:

https://abdelazimhussien.github.io/MetaheuristicsAlgorithms.jl/dev/cec.html#MetaheuristicsAlgorithms.F1

It would be better to use the package-defined methods, e.g., F1(x) in this case to produce the figures.