introduce a configure dot split penalty

Given this file:

```python
l = {
'foo': {
'bar':
re.compile(r'lllllllllllllllllllllllllllllllllllloooooooooooooooooooooooolllllllllllllllllllllllllllllllllllll'),
}
}
```

## Config 1

```ini
[style]
based_on_style = pep8
column_limit = 80
dedent_closing_brackets = true
```

Output is fine:

```python
l = {
'foo': {
'bar':
re.compile(
r'lllllllllllllllllllllllllllllllllllloooooooooooooooooooooooolllllllllllllllllllllllllllllllllllll'
),
}
}
```

## Config 2

```ini
[style]
based_on_style = pep8
column_limit = 120
dedent_closing_brackets = true
```

Output is uglier:

```
l = {
'foo': {
'bar':
re.
compile(r'lllllllllllllllllllllllllllllllllllloooooooooooooooooooooooolllllllllllllllllllllllllllllllllllll'),
}
}
```

The first output would have been prettier: having the string alone, rather than splitting before a dot. Maybe adding a configurable penalty for dot splitting would help? Or just output the first directly?