Add apiVersion as a public parameter

[AlessandroDeidda]

const ( apiVersion = "v62.0" )

It would be helpful to have more control over the API version.
This could be done by adding a parameter to the Init method or to the Creds struct so that it can be used from the authentication process.

[k-capehart]

@AlessandroDeidda Yeah, I've thought about this. I think adding it to the Creds struct as an optional value is a good idea. If provided, then it can override the default.

If you want to submit a PR for it then feel free, otherwise I'll try to get to it in the next couple weeks.