background style - not ready to merge

Hi all,

This is my next installment of addressing #711.

This branch works as expected and is almost ready to go in . . . except for a broken spec. (Comments in-line) Has to do with resource disposal . . . perhaps @jasonrclark can help? :)
You can make a corners method that just delegates to the DSL object's curve.

E.g.:

```ruby
def corners
  dsl. curve
end
```

Although rewriting the painer to use curve is probably better, but that would affect too much s I wouldn't want to do that in this PR.