Add Buffer::beginp() and Buffer::endp()

src/core/Buffer.h

@@ -177,7 +177,9 @@ public:
             const Buffer::Iterator & end);
     std::shared_ptr<std::string> filename() const { return m_filename; }
     Iterator begin() const { return Iterator(this); }
+    std::shared_ptr<Iterator> beginp() const { return std::make_shared<Iterator>(this); }
     Iterator end() const { return *m_eof_iterator; }
+    std::shared_ptr<Iterator> endp() const { return std::make_shared<Iterator>(*m_eof_iterator); }
     void push_operation() { m_operation_level++; }
     void pop_operation();
     void undo();