Add token/password authentication to ruby client

[renier]

To get a client that will use token-based authentication headers, simply obtain a client using a password like this:

    client = SoftLayer::Client.with_password(username: 'foo', password: 'bar')
    puts client.authentication_headers
    puts client['Account'].getCurrentUser

I increased the version to 3.2, since, follwing semver rules as I understood them, this is not a bug fix but rather a backwards-compatible enhancement.