Function normalize 

pub fn normalize<'a>(ctx: &AtomArena<'a>, atom: Atom<'a>) -> Atom<'a>

Normalize an atom into canonical form.

The result is allocated in the same arena as the input via ctx.

Example

use ocas_atom::normalize::normalize;
use ocas_atom::AtomArena;
use ocas_core::arena::Arena;

let arena = Arena::new();
let ctx = AtomArena::new(&arena);
let x = ctx.var("x");
let y = ctx.var("y");
let z = ctx.var("z");
let inner = ctx.add(&[x, y]);
let outer = ctx.add(&[inner, z, ctx.num(2), ctx.num(3)]);
let result = normalize(&ctx, outer);
assert_eq!(result.to_string(), "5 + x + y + z");