CLI tool: changelog browser

Let's you query the changelog of a github repository or npm package. Shows it using `less`, like a `git diff`.

```sh
$ changed andywer/key-store
$ changed npm:key-store
$ changed npm:key-store 0.2...1.0
```

## How it works

- Reads GitHub releases
- Fallback: Use unpkg.com to look for a `CHANGELOG.md`