Pycups

* Bindings for streaming API: cups.CUPS_FORMAT_* constants, cups.createJob(),
cups.startDocument(), cups.writeRequestData(), cups.finishDocument().

* Python 3 support.

* cups.connectDest() API fix: now returns a tuple.
* cups.enumDests(), cups.connectDest(), and cups.CUPS_DEST_FLAGS_*
constants (requires CUPS 1.6).

* cups.IPPError tuple now contains the specific error string, if one
is available.

* Define all constants regardless of which version of CUPS is built
against.

* New constants from 1.5:
- IPP_AUTHENTICATION_CANCELED
- IPP_PKI_ERROR
- HTTP_NOT_IMPLEMENTED
- HTTP_BAD_GATEWAY
- HTTP_SERVICE_UNAVAILABLE
- HTTP_GATEWAY_TIMEOUT
- HTTP_NOT_SUPPORTED
- HTTP_AUTHORIZATION_CANCELED
- HTTP_PKI_ERROR