Omxplayer-wrapper

* Clean up process when start up fails (196)

* Remove unused imports (`mock`) causing errors (157)

* Remove `tests` package from distribution
* Support calling `quit` multiple times without raising exception

* Change `set_volume` to work with values between 0-10 instead of
millibels
* Fix `volume` to return actual volume rather than just 1.0
* Fix `rate` to return actual rate rather than just 1.0
* Support providing arguments as a `str` which is then split with `shlex.split`,
i.e. you don't have to provide a list of shell split args if you don't want to.
* Support `str` media file path in `OMXPlayer` constructor.
* Cleanup omxplayer process on exit

* Correct `omxplayer.__version__` to return 0.2.5 instead of 0.2.3 (in 0.2.4)

* New methods:
* `aspect_ratio`
* `can_raise`
* `fullscreen`
* `has_track_list`
* `height`
* `hide_subtitles`
* `hide_video`
* `metadata`
* `next`
* `previous`
* `rate`
* `select_audio`
* `select_subtitle`
* `set_rate`
* `show_subtitles`
* `show_video`
* `supported_uri_schemes`
* `video_pos`
* `video_stream_count`
* `width`
* We no longer verify the source exists before playing to allow a broader range
of valid inputs
* Revamped docs, available at http://python-omxplayer-wrapper.readthedocs.io/

Developer relevant changes

* Added integration tests
* Refactored tests
* Unit testing on python 3.5 and 3.6 in travis