Relationship of international law and municipal law — Treaties — United Nations Convention against Torture, 1984 — Status in international law — Zimbabwe not party to Torture Convention — Extradition Act — Article 3 of Torture Convention — Non-refoulement principle — Whether Article 3 of Torture Convention applicable in Zimbabwe — Universal prohibition of torture — Customary international law — International Covenant on Civil and Political Rights, 1966 — African Charter on Human and Peoples' Rights, 1981 — Interpretation — Zimbabwe party to International Covenant and African Charter — Zimbabwe’s obligations under International Covenant and African Charter — Whether substantial grounds for believing appellant at risk of being subjected to torture if extradited — Whether appellant’s extradition prohibited under Extradition Act — The law of Zimbabwe