add Buffer::Iterator::clonep()

src/core/Buffer.h

@@ -102,6 +102,10 @@ public:
         }
         size_t line() const { return m_line; }
         size_t offset() const { return m_offset; }
+        std::shared_ptr<Iterator> clonep()
+        {
+            return std::make_shared<Iterator>(*this);
+        }
 
     protected:
         friend struct Range;