simplify the update of test files

[ThomasBreuer]

As far as I understand, the test files for the package get updated via the instructions in tst/generate_tst_files.g.
These instructions themselves would have to be updated, but I think it would be better to use AutoDoc's extract_examples := true option (which is available in the AutoDoc version that is required by makedoc.g) instead.

[fingolfin]

Yeah this is very complex, see also the content of the examples dir.

I guess part of it was a desire to also be able to update the examples in the XML files. Do we have capabilities for that? In any case, in my experience this is not so common so I'd not be worried about loosing it.

I thought about cleaning this up at some point but gave up because there were so many levels of indirection :-/.