File: extract read_file function which returns file content in a string

src/file.cc

@@ -13,7 +13,7 @@
 namespace Kakoune
 {
 
-Buffer* create_buffer_from_file(const std::string& filename)
+std::string read_file(const std::string& filename)
 { 
    int fd = open(filename.c_str(), O_RDONLY);
     if (fd == -1)
@@ -35,6 +35,12 @@ Buffer* create_buffer_from_file(const std::string& filename)
         content += std::string(buf, size);
     }
     close(fd);
+    return content;
+}
+
+Buffer* create_buffer_from_file(const std::string& filename)
+{
+    std::string content = read_file(filename);
 
     if (Buffer* buffer = BufferManager::instance().get_buffer(filename))
         BufferManager::instance().delete_buffer(buffer);

src/file.hh

@@ -23,6 +23,7 @@ struct file_not_found : file_access_error
 };
 
 class Buffer;
+std::string read_file(const std::string& filename);
 Buffer* create_buffer_from_file(const std::string& filename);
 void write_buffer_to_file(const Buffer& buffer, const std::string& filename);