Use package-changed

[thdk]

For one of my upcoming projects I needed to simply know if the package was changed or not. My use case was not related to installing packages so I exctracted the code for that to package-changed which I'll be using in my project.

Since package-changed contains the core (converted to typescript though) of install-changed I submit this PR in case you would be interested in using it as a dependency so you could reduce maintenance work on install-changed. I noticed it has been one year since its last release on npm and merged pull requests dont get released so I understand you probably have other things on your mind than maintaining and releasing new versions for this package.

If you have thoughts, please let me know.