KEM combiner reduction

[ounsworth]

I wrote a paragraph that does a security reduction of this KEM combiner to draft-ounsworth-cfrg-kem-combiner.

[ounsworth]

@HBrock I wrote some text, but I am not very familiar with the XML I-D format. Are you willing to add the cross-references, and move some of that text into an appendix?

[HBrock]

@HBrock [...] move some of that text into an appendix?

Thank you for your proposal. I will merge it. Should I move the text to a new Section 8.8 or should I introduce a new Appendix C?

[HBrock]

I will merge your changes. After the merge I will update the references and move the second paragraph to the Security Considerations section.