A crate containing a singly-linked list.
As of 0.4.1, cons-rs supports `#[no_std]` environments.
Note that it still depends on the `alloc` crate.
This version is a **full** rewrite of the entire crate.
It has migrated from its past as a "list of nested pairs"
to what it has actually been the entire time, a singly-linked list.
The main reason I didn't publish this as a new crate is because
all the names are taken, and the *use cases* are mostly the same.