Provide a command line interface for updating deps

This provides the following:
```
$ closure-util --help

Usage: closure-util <command> [options]

command     
  update-compiler     Update the Compiler
  update-library      Update the Library
  update              Update both the Library and the Compiler

Options:
   -l LEVEL, --loglevel LEVEL   Log level  [info]
```

When the `closure-util` package is installed as a dependency of another, the `closure-util` utility will be installed as an executable.  In cases where `closure-util` is a direct dependency or a transitive dependency, the `closure-util` utility will be available to [`npm` scripts](https://www.npmjs.org/doc/misc/npm-scripts.html) (so you don't need to know the path to it, it will be added to the `PATH`).