CLI should load version from JAR

Right now, the Formulog version is hard-coded into the CLI, which is easy to forget to update (see #25). Instead, the version should be stored in the JAR (and maybe the git commit as well), and then we can load it programmatically from the CLI code. See:

* https://github.com/remkop/picocli/issues/757
* https://stackoverflow.com/questions/37476898/read-last-commit-of-the-git-and-commit-number