Pod::Weaver plugin to check for duplicate Pod section headers

 Pod::Weaver::Plugin::EnsureUniqueSections is a Pod::Weaver plugin to
 ensure that the Pod after weaving has no duplicate top-level section
 headers. This can help you if you are converting from writing all
 your own POD to generating it with Pod::Weaver. If you begin
 generating a section with Pod::Weaver but you forget to delete the
 manually written section of the same name, this plugin will warn you.