SpaceBeforeBrace: Add config param to allow extra spaces in single line blocks.

This allows you to space out single line blocks to make the scss more easily scanned by humans:

```scss
.icon-up            { &:before { content: '^'; } }
.icon-down          { &:before { content: 'v'; } }
.icon-left          { &:before { content: '<'; } }
.icon-right         { &:before { content: '>'; } }
```

My first ever Ruby code, so please let me know if there's a more elegant way to do this!