Cython API: Added an __iter__ method to the class Column_line (iterating

on the elements names) (previously an iteration would work but with
unexpected results)

python/obitools3/dms/column/column.pyx

@@ -325,6 +325,14 @@ cdef class Column_line :
         return str(self._column.get_line(self._index))
  
     
+    def __iter__(self) :
+        cdef list  elements_names
+        cdef bytes element_name
+        elements_names = self._column.elements_names
+        for element_name in elements_names :
+            yield element_name
+        
+    
     cpdef update(self, data):       # TODO ?????
         if isinstance(data, dict):
             data=data.items()