Replaces the use of `BTreeMap` and `HashMap` for maps and records with
`Vec<(Keyword, Value)>` and `Vec<(Keyword, StaticType)>`. This
simplifies the data structure and allows for ordered iteration, which is
important for serialization and comparison.
Also updates the `unpack` function in `vm.rs` to handle records as well
as lists when destructuring.
Michael Schimmel