Move some more examples from PGFPlotsXExamples.jl to the manual

[KristofferC]

There are a few examples in

https://github.com/KristofferC/PGFPlotsXExamples/tree/master/examples

that might be good to move to the manual. There are probably some redundant ones but a few of them show some things that might be interesting to have in the manual.