Elaborate substring queries

Example query:

```ts
q.str(
  q.str(),
  ':',
  q.str(),
  ':',
  q.alt(sym(), str()),
  q.opt(q.str('@').q.str())
);
```

It should match strings like `"com.example:package:1.2.3"` and `"com.example:package:${packageVersion}@ext"`.