Remove arrow depencency

[netrounds-fredrik]

I think this looks like a nice and simple library for parsing m3u8 playlists, but one thing that kind of ruined that impression was when I realized that it depended on arrow. I'm not saying arrow is a bad library, but it's way to big (with all it's own dependencies) for what it's used for in this project.

Currently arrow is used for two operations:

• One in parser.py: arrow.get(value).datetime...
• ... and one in models.py: arrow.get(self.program_date_time).isoformat()

So it's basically parsing and formatting date and times in ISO 8601 format. A more lightweight library without additional dependencies for parsing ISO 8601 is https://pypi.python.org/pypi/iso8601. The operations currently done with arrow can be done like this with iso8601:

• iso8601.parse_date(value)
• self.program_date_time.isoformat()

Completely removing parsing (just providing the value as a string) or making it optional is another way to go.

[flavioribeiro]

@netrounds-fredrik +1 on this. Would you mind sending a pull request?

[netrounds-fredrik]

Created a pull request. All unit tests passes.

[netrounds-fredrik]

I see that arrow has been reintroduced as dependency for the unit tests in f50cad5. What was the reason for this?