Unnecessary super-directory for the plotting-examples in documentation

[Liameloy]

Introduced with #67

Currently, when trying to view example-plots in documentation one has to navigate through:
'Examples' -> 'Plotting Examples' -> 'plotting'

Ideally the last tab should not exist and example-plots be viewable under 'Plotting Examples'

[pjaap]

related to j-fu/ExampleJuggler.jl#19

[pjaap]

After merging #75 this problem still exists...

[j-fu]

You can call cleanexamples() after makedocs() to remove these directories.

The point creating them is the fact that the markdown files generated by ExampleJuggeler need to be in subdirectores of docs/src in order to be found by Documenter.

[Liameloy]

I will test that and if it works then this is done. My understanding is that this extra tab on the wabpage is not caused by the subdirectory 'script_examples' under docs/src but that there is another directory in docs/src/script_examples called 'plotting' in which the index.html for the webpage is stored.