Implement `--version` command line parameter

[happybeing]

The code already has cli parameters to use when authenticating (using yargs, see ./bin.js).

The most important one to add is --version, which should report the version specified in package.json.

At the same time it would be sensible to add --help which should report the version and give some basic information about the command.

We can leave explicit mount control parameters until later, but the idea is that you can either run without those and get defaults, or you can give a series of 'mount this here with optional permissions' type instructions from the command line, or perhaps a config file that is specified on the command line.