Creates a new row at position.
If parent is non-null, then the row will be made a child of parent. Otherwise, the row
will be created at the toplevel. If position is -1 or is larger than the number of rows at that level, then the new row will
be inserted to the end of the list. iter will be changed to point to this new row. The row will be empty after this function
is called. To fill in values, you need to call @set or
set_value.
| this | |
| iter |
An unset TreeIter to set to the new row |
| parent |
A valid TreeIter, or null |
| position |
position to insert the new row, or -1 for last |