Option to disable removal of line breaks

I would like to hinder YAPF from removing line breaks only because the column limit is not reached, e.g. not to change

```
# column limit --v
my_class_instance.variable_a = my_function(
value="this_is_usually_a_really_long_argument")
my_class_instance.variable_c = my_function(
value="this_is_usually_a_really_long_argument")
my_class_instance.variable_b = my_function(
value="this_is_a_short_one")
my_class_instance.variable_d = my_function(
value="this_is_usually_a_really_long_argument")
```

to

```
# column limit --v
my_class_instance.variable_a = my_function(
value="this_is_usually_a_really_long_argument")
my_class_instance.variable_c = my_function(
value="this_is_usually_a_really_long_argument")
my_class_instance.variable_b = my_function(value="this_is_a_short_one")
my_class_instance.variable_d = my_function(
value="this_is_usually_a_really_long_argument")
```

At first I thought `JOIN_MULTIPLE_LINES = False` would do the trick, but it seems it doesn't. What are your thoughts on this?