* Implement more methods in Resources.php to complete API.
* Refactor tests:
  - create a test class for each .php file instead of one huge one for
    everything
  - maybe too much code duplication in the test, but is it better that way to
    keep the tests loosely coupled?
* PEAR coding standards compliance
* Look into using URLs instead of piecing together a path from sid/basename/etc
* Title-cased properties e.g. $client->SmsMessages and $client->Account->Calls->Notifications
* Intelligent type mapping e.g. dates in the object get converted to DateTime objects