Add syntax for tuples and re-enforce homogenous arrays.

Hurray for tuples! This PR also brings back homogenous arrays, which I would prefer, and the addition of tuples solves any decent use cases for mixed types.

```toml
(1, "tom", "staff")  # Perhaps some UNIX account info.
(2.48, 9.37, 28.81)  # Or maybe x/y/z coordinates.
```