add Buffer::clear() and Buffer::set_string()

src/core/Buffer.h

@@ -119,7 +119,9 @@ public:
         m_cursors.push_back(iterator);
         return iterator;
     }
+    void clear() { m_gap_buffer->clear(); }
     auto get_string() { return m_gap_buffer->get_string(); }
+    void set_string(const std::string & s) { m_gap_buffer->set_string(s); }
     size_t size() const { return m_gap_buffer->size(); }
     uint8_t * address(size_t offset) const { return m_gap_buffer->address(offset); }
     Encoding::Type encoding() const { return m_encoding; }

src/core/GapBuffer.cc

@@ -62,7 +62,7 @@ std::string GapBuffer::get_string()
     return std::string((char *)m_buffer, m_size);
 }
 
-void GapBuffer::set_string(std::string s)
+void GapBuffer::set_string(const std::string & s)
 {
     clear();
     insert(0u, (const uint8_t *)s.c_str(), s.size());

src/core/GapBuffer.h

@@ -72,7 +72,7 @@ public:
     /**
      * Replace the buffer contents with a string.
      */
-    void set_string(std::string s);
+    void set_string(const std::string & s);
 
     /**
      * Get the size of the data stored within the buffer.