How to specify `doctestfilters` for the function `doctest`?

[ThomasBreuer]

The function makedocs supports the keyword argument doctestfilters.
This is a documented feature, and it works nicely when one runs the doctests as one step of processing the documentation.
However, if one wants to run the doctests by calling doctest in a @testset then doctestfilters seem to be not supported; doctest calls makedocs but does not supply keyword arguments such as doctestfilters.

[mortenpi]

That sounds like an oversight on my part -- we should at least allow passing doctestfilters as an argument to doctest, that would then get passed on makedocs.