Modify and improve examples

[hecatia-elegua]

I would like to improve example code a bit, e.g. remove the weird array/tuple nested one since that's available in tests now.
Then also include the expanded output, adding code comments to either all generated code or only to one example expanded output.

Idea came from:
https://github.com/taiki-e/pin-project/blob/HEAD/examples/struct-default-expanded.rs

Note: These generated code examples are the little simplified version of the actual generated code