Idea: Stitch-functions

(Originally posted by @joningold on our internal Asana.)

```
=== knot ===
= function some_logic
...
= normal_stitch
{ some_logic(): Content. }
```

Main reason being - the function can then reference other stitches inside the knot without having to use the full address. It's not scoped, exactly - the function could be called from other knots, or reference other knots - but it helps keep logic for a knot inside the knot.

So; if this is easy, I think it'd be good. But if it's complex, it's no big deal.

The issue names no files, tests, or entry points. Start by locating the parser and resolver for knots and functions, then determine how the proposed syntax should resolve stitch references and what tests would demonstrate that functions can use nearby stitches without full addresses.

Written by the indexing model from the issue text.