extend empty slice

I see the empty slice section
https://github.com/quasilyte/go-consistent#empty-map

does it make sense to include a `var` initialisation too? eg

```go
	a := make([]int, 0)
	b := []int{}
	var c []int
```

https://play.golang.org/p/oI0oilKpgg7