array item access?

lodash.get allows for something like this:

```js
get(obj, 'foo[0]')
```

which would correspond to:

```js
obj = {
foo: [
'x' // <-
],
}
```

Any chance this could be supported in dlv as well?

Start by reading dlv's existing dot-separated property-path handling and compare the requested `foo[0]` form with lodash.get's behavior. Done means `dlv(obj, 'foo[0]')` returns the first array item while existing deep-property access continues to work; add or update the relevant tests if the project has them.

Written by the indexing model from the issue text.