Documentation : Tutorial improvement...

Refactoring examples on implementation of generics for linked list.
Fixing typo of 'Note's for coherancy.

Adding internal links inside the tutorial example with traits,
generics etc...
Minor modifications to Axel's tutorial improvements (see also #12472).
auto merge of #12599 : pnkfelix/rust/fsk-issue12472-tutorial-improvement, r=pnkfelix

Minor modifications to Axel's tutorial improvements (see also #12472).