Merge pull request #45 from ticosax/master

Tackle some issues
Implement timeout support for pyipptool
Install ipptool
Merge pull request #46 from ticosax/timeout-subprocess

Timeout subprocess
99% coverage
Try https://coveralls.io
Merge pull request #47 from ticosax/extend-test-coverage

Extend test coverage
Adjusted get_subscriptions to conform to RFC 3995
Merge pull request #51 from sbellem/get-subscriptions

Adjusted get_subscriptions to conform to RFC 3995
Implemented Cancel-Subscritpion operation
Merge pull request #52 from sbellem/cancel-subscriptions

Implemented Cancel-Subscritpion operation
Fixes #55
Merge pull request #56 from sbellem/issue-55

Fixes #55
Better description with some useful keywords