feat: set up project skeleton for new CLI

[danxmoran]

Closes #2

• Set up go modules, using Go 1.16
• Add the entry-point for the CLI, with the version command implemented
• Add our standard linting tools/scripts
• Add a Makefile to be the source-of-truth for build/test/lint commands
• Add a basic CircleCI workflow

[danxmoran]

Eventually we might want a pre-step to cache dependencies. If we hit that point, we'll need to deal with golang/go#43994

[danxmoran]

Risking an innovation token on urfave/cli over spf13/cobra. cobra has always felt more heavyweight/verbose to me than a CLI parser needs to be. cli looks very similar to the kit/cli convenience wrapper in influxdb.

If we hit a wall with it, we can fall back to using cobra and copy the code from influxdb.