Omit explicit pass goroutine

```swift
go {
    $0.select(...)
}
```
`$0` may cause unsafe use case (eg. pass it outside the closure or use it in another goroutine)
It also prevent to implement `<-` operator

We need define a static function something like:
```swift
func getG() -> Goroutine! {
    // return current goroutine like
    // Thread.current
}
```

