First release of `sopel-npm` with:
* `npmjs.com` package link handling, with and without a version number
* `.npm` command for text search of packages in the registry
Known issues:
* Packages' publication times are not displayed, because the NPM registry's
package-version endpoint inexplicably does not provide a release timestamp.
* While all of the error-handling code paths _should_ work, in theory, some
haven't been verified in real-life testing yet.