Package metadata: link to changelog and/or version release notes

[saltire]

As a package consumer, it might be nice to have a direct link to either the changelog for a package, or the release notes for its latest version.

This could possibly be a field in package.json, linking to the changelog file. In cases where the package repo makes use of e.g. the Releases feature on GitHub, this could be a dynamic link like https://github.com/org/project/releases/tag/v{version}.

On the package's NPM page, this could be linked from the Version text on the sidebar. It could also potentially enable some quick info lookups, or at least links, from the CLI.

I noticed a similar suggestion at #505, but this seems like it could be a much easier add for most maintainers, and could still save consumers some time when new versions are released.

[larsnystrom]

Could we also please have a link to this in the output of npm outdated? That'd save so much time when updating major versions of npm dependencies.