New utility rmdocs

[astrozot]

This pull request introduces a new utility function, rmdocs, which can be used to remove Core.@doc macro calls, leaving only the associated definition. For example

julia> ex = quote
  "A simple function that duplicate its argument."
  function f(x)
    return 2x
  end
end;

Then one has

julia> MacroTools.prewalk(MacroTools.rmlines ∘ MacroTools.rmdocs, ex)
quote
    function f(x)
        return 2x
    end
end

[cstjean]

Sounds good to me. Could you add tests, please?

[astrozot]

Thank you for your fast reaction @cstjean. I added the tests for rmdocs, but since I have not seen tests for the similar function rmlines, I also added tests for this one.

[cstjean]

Great PR, thanks!