- organize examples better
- add an example illustrating behavior if element type is a named pointer type
- both compilers and go/types (per https://go-review.googlesource.com/33358)
  follow this now

See the issue for detailed discussion.

Fixes #17954.

Change-Id: I8d90507ff2347d9493813f75b73233819880d2b4
Reviewed-on: https://go-review.googlesource.com/33361Reviewed-by: Rob Pike <r@golang.org>