Splatted objects

We already got splatted arrays `[a, b...]`. Now how about extending it to objects?

```
coffee> o = un: 42; console.dir {0: 1, o...}
{ '0': 1, un: 42 }
```

The compilation of `{0: 1, o...}` would be something like:

```
__mix({0: 1}, o)
```

where `__mix` is defined as:

```
(target, source) ->
  target[k] = v for k, v of source
  target
```
