`Locator::configure` should take `self` by `&mut`

[zsol]

If I understand the Locator trait correctly, configure should be used to store information in the locator instance:

    /// Configures the locator with the given configuration.
    /// Override this method if you need to have some custom configuration.
    /// E.g. storing some of the configuration information in the locator.
    fn configure(&self, _config: &Configuration) {}

But its signature suggests it doesn't mutate self. Is that on purpose? I would normally expect the signature to look like:

    fn configure(&mut self, config: &configuration) {}

Which would make it clear that configure mutates the instance.