Command Interface

This isn't ready for merge yet, PRing for code review/comments.
I'm not sure these work. (and some obviously cant because of multiple options in one blob (`-abc`))

```sh
cmd --foo bar baz   # cmd, { foo: bar }, [baz] 
cmd -foo bar baz    # cmd, { foo: bar }, [baz]
cmd -foo=bar baz    # cmd, { foo: bar }, [baz]
```

1. I think that we can forgo `--key val` in favor of always `--key=val`
2. but we should accept `-key=val` too (not unixy, but golang idiomatic, everybody uses it).
3. And, if 1. and 2., we don't clash with multi-opt-in-one (`-abc`), because `-key=val` requires `=`.