Added logging for response content.
Refactored payment for class.

The complete_transaction function also now fails nicely if the http
request times out, or if TrustCommerce returns an empty response.
Updated logging to log query string of returned transactions.
Improved transaction logging.
Modified get_token_response to use multiple attempts if the api is unavailable.
Modified transaction handling.

The api will return empty responses if the same token is processed
more than once. The logic has been updated to handle this the same way
as a mismatched hash.
Increased sleep interval for get_token failures.

Also added response logging for easier debugging.