Add uc_dstr_copy

include/ucore/dstr.h

@@ -40,6 +40,15 @@ void uc_dstr_init(struct DStr *str);
  */
 void uc_dstr_destroy(struct DStr *str);
 
+/** Copy a DStr
+ *
+ * @param dest destination string to copy to, must not contain an existing string
+ * @param src DStr to copy
+ *
+ * @return 0 if success, != 0 if allocation fails
+ */
+int uc_dstr_copy(struct DStr *dest, const struct DStr *src);
+
 /**
  * @return the available/unused tail bytes in the string.
  */