vim: Tweak how comment nesting works

Don't try to match line comments inside of a comment block. That makes
no sense and can highlight differently for people who override their
highlights.

Similarly, don't match a doc-comment inside of a comment block. It
shouldn't be highlighted differently unless it's actually a doc-comment
(and nested comments are obviously not doc comments).

Fixes #12307.
Mark top level module as a crate in rustdoc, closes #12507
Remove unused type_is_pod function
Implement `has_dtor` method in TypeContents
Keep track of Enum's with destructors
Forbid moves out of static items Closes #10577
Replaced @List with ~List in Rust's recursive example
Renamed variables
Implement Eq for Cell<T>
Modified list::from_vec() to return List<T>
Implemented Items<'a, T> for List<T>
Replaced list::each with iter() in Arenas's Drop impl
Replaced list::each with iter() in get_region
Removed list::foldl() in favor of iter().fold()
Removed list::find() in favor of iter().find()
Removed list::any() in favor of iter().any()
Implemented list::len() based on Container trait
Implemented list::is_empty() based on Container trait
Removed deprecated list::{iter,each}() functions
Replaced list::has() with list::contains()