Add a script to run 'go vet'

@filbranden 
Is it really worth filtering out the "exit status" lines?

If so, I recommend:

```shell
  vet_output=$(go vet "${goflags[@]:0}" "./${arg}" 2>&1) || {
    something_failed=1
  }
  echo "${vet_output}" | grep -v "^exit status "
```

You might consider that "go vet" sends its output to stderr, so maybe it would make sense to redirect the grep output to stderr as well (?). I think I'd just keep the "go vet" output unmodified though.