Add write_file () syscall, CE implement redirections, libarena arena_realloc ()

libsystem/system.h

@@ -84,4 +84,7 @@ int read_dir_entry (const char* path, struct dir_entry* entry, size_t entry_num)
 /* create a file */
 int create_file (const char* path);
 
+/* write to a file */
+int write_file (const char* path, size_t off, uint8_t* buffer, size_t size);
+
 #endif // _LIBMSL_M_SYSTEM_H