Add slt-changelog command

Hey, you got Ruby in my JavaScript\!
Add slt-stage command

Publishes to registry using MAX(v.local, v.registry)+0.0.1
Add --summary option to slt-changelog

Prints to stdout the list of changes ince the previous release
Change slt-changelog --unreleased to --version VERSION

To generate a changelog for an unreleased version, possibly during the release process
1.1.0