arrow_spacing should allow you to force 0 spaces on each side

Proposed coffeelint config setting
```
"arrow_spacing": {
    "level": "error",
    "spacing": {
      "left": 0,
      "right": 0
    }
  },
```

Good: 
```
foo =()->
```

Bad
```
foo = () ->
foo = ()->
```

I will make a pull request for this. I will use it in my project but are you interested in having that in this? Should I make a pr?