Stream cookbook

**NOT FOR MERGE**

Just a quick preview, WIP. Feel free to recommend new recipes.
I did some tricks around these situations like so:

```
val thing = 32

new X {
//#the-thing
val thing: Int = ???
//#the-thing
}

//#the-thing
using(thing)
//#the-thing
```

Not sure if it's worth it here, feel free to ignore