Add a test for array-based configuration, add docs


    Some of our other supported config formats support arrays for the
    values of the data, but it will generally be made available as
    arrays of strings.  This commit adds a minor tweak so that
    we will call `symbol` on these strings before using them, and
    adds a test validating that this type of configuration will
    work properly.
    
    The commit also adds documentation for the new setting.