Explain potentially confusing string example.

Reported be @ElBaha
Fix span.
Note that Rust can be embedded.
Add a link to the wiki's package list and refer to git
Fix grammar error.
Add rustdoc documentation.
Fix tiny formatting error.
Clarify that strings aren't magical.
Clarify `as`, mention transmute.
Fix tiny formatting error.
Macro definition is feature gated.
Wildcard changes.
loop -> continue
Inherited mutabilty clarification

Also no longer reference mutable fields
Clarify arity
Clarify newtype
Function declaration takes pats, not exprs.
Update Owned to Send, show some types which aren't
Tiny fixes to linked list section.
Update `Freeze` information