Python4yahdlc

* Add [yahdlc][yahdlc] library as sub-module
* Update [yahdlc][yahdlc]'s version to [1.1.0][yahdlc v1.1.0]
* Fix the use of objects with the same name as a built-in
* Improve the comments
* Improve the documentation

[yahdlc]: https://github.com/bang-olufsen/yahdlc

* Use the [build stages feature][build stages] of [Travis CI][travis ci]

[build stages]: https://docs.travis-ci.com/user/build-stages/
[travis ci]: https://travis-ci.org/

* Return the sequence number to be sent back as `NACK` when an FCS error is raised
* Replace tab characters with spaces
* Improve comments

* Deploy automatically the new releases to [PyPI][pypi] using [Travis CI][travis ci]
* Improve the packaging

[pypi]: https://pypi.python.org/pypi
[travis ci]: https://travis-ci.org/

* Use the `README.md` file as package's long description

[yahdlc]: https://github.com/bang-olufsen/yahdlc