Add `string` support and update for the lastest cranelift.

[Cy6er7um]

1. Add string support, now you can use "Content" in the toy language.
2. Add symbol log, you can use it to print content to the console.
3. Replace fn -> extern fn.
4. Update the examples.
5. Format the code.
6. Update for the lastesr cranelift (0.84).
7. Add test.yml

[Cy6er7um]

Do I need to do anything else?

[bjorn3]

LGTM, but I don't have merge permission, so someone else will have to merge it.

[Cy6er7um]

LGTM, but I don't have merge permission, so someone else will have to merge it.

Thanks!