Allow multiple subcommands

I would really like to be able to do the following:
```
prog cmd1 cmd2
```
Because my program needs to have a CLI to run commands seq sequentially, without duplicating all the fields in each subcommand: Currently the cli for that looks like:
```
prog cmd1 --cmd2
```
Which makes everything really awkward, especially because I have to duplicate the fields and support chaining and calling of `cmd2` directly. And now I want to be able to chain arbitrary number of commands, this gets very hairy!
So please, can we allow multiple subcommands? :)