Version 2.3 of the SOAP API can be safely used

The difference between version [2.2][2.2] and [2.3][2.3] of the WSDL contract<sup>†</sup> is subtle enough not to affect the current codebase.

<sup>†</sup>_addition of `activityNameFilter` to the `GetLeadChanges` params and the removal of `skipActivityLog` from the `ListOperation` params_

  [2.2]: http://app.marketo.com/soap/mktows/2_2?WSDL
  [2.3]: http://app.marketo.com/soap/mktows/2_3?WSDL