feat: add match as a subclass of event

[Olen]

Should fix Olen/Spond#112

Not tested, just getting it out of the way for now

[elliot-100]

Thanks @Olen.

I have added tests based on your example in Olen/Spond#112.

I think the output from Match.__str__ could perhaps be improved. At the moment it is very similar to an Event, e.g:
Match(uid='M1', heading='Match One', start_time: 2021-07-06 06:00:00+00:00, …)

I would think match_info.opponent_name and maybe match_info.team_name and match_info.type should be in there.

But I don't know what heading looks like for a real match.

[Bart274]

Looks good

[elliot-100]

@Olen or @Bart274 do you know if any of these fields aren't always present? e.g. scores for a future match.

If so they should be optional on Match creation.

[elliot-100]

I've tested with a minimal future match and works fine.