Allow CLI to be installed globally

I should be able to do:

```sh
npm i -g lolcode
```

And then run:

```sh
lolcode HELLO.lol
```

To get my `HELLO.lol` to run.

This can be achieved using the [`bin`](https://docs.npmjs.com/cli/v7/configuring-npm/package-json#bin) option in the `package.json`.