Add :string support for `fetch`

[drkameleon]

It would be great if fetch, instead of an array of attributes could also take a string (or literal?) against a pre-defined(?) record field, e.g. name or title.

For example:

fetch'person [name: "John"]

would be equivalent to:

fetch'person "John"

This would help make longer queries less verbose and less visually-cluttered.

---

Compare this: (even when using helpers)

person [actedIn: movie [title: "Memento"], isFrom: country [name: "Australia"]]

To this:

person [actedIn: movie "Memento", isFrom: country "Australia"]

[drkameleon]

Ready to merge 🚀