Restructure sb tool to allow for top-level calls

Previously all commands would be called via
```
$ sb <flags> sh
? <command>
```

This patch allows commands of the form
```
$ sb <flags> <command
```

These commands are understood by cmdline, so you can
```
$ sb help command
```
or
```
$ sb <flags> sh
? help command
```

Change-Id: Ia6bb970401eecba57c4a5b5570550149182cb841
10 files changed
tree: 8491d5172e0c5d2e93b7ab829bb7c72f4c10a055
  1. cmd/
  2. examples/
  3. internal/
  4. lib/
  5. runtime/
  6. services/
  7. test/
  8. .gitignore
  9. AUTHORS
  10. CONTRIBUTING.md
  11. CONTRIBUTORS
  12. envvar.go
  13. envvar_test.go
  14. LICENSE
  15. PATENTS
  16. README.md
  17. VERSION
README.md

Vanadium

This repository contains a reference implementation of the Vanadium APIs.

Unlike the APIs in https://github.com/vanadium/go.v23, which promises to provide backward compatibility this repository makes no such promises.