v0.5.7

Added

• VecDeque<T> assertions for membership, negative membership, ordered exact contents, unordered exact contents,
  predicate matching, and length checks, matching existing Vec<T assertions.

Changed

• Switched remaining places to use self.fail(|w: &mut String| { writedoc! {w, r"..."} }) over format_args! style
  assertion violation reporting, improving readability and maintainability of user-facing messages.