Error Handling

[Pluriscient]

When encountering an error in the request, like a 404 when getting a player, the api currently throws an error. As throwing errors is quite expensive, I would prefer for there to be a way to handle these request exceptions myself, like being able to pass an error handler to the client, or perhaps being able to pass a custom apirequester.

[AeonLucid]

Being able to pass an error handler sounds good, but I don't have experience creating something like that.
If you want to make a PR or work out the idea more, go ahead.

[Pluriscient]

At the moment there are two main ways of handling this that I'm thinking of:

• add an argument to the constructor of the ApiRequester as Func<HttpResponseMessage> which will then be called when there isn't a successful response while null is returned.
• Allow for a custom ApiRequester to be passed to the RLSClient
  Currently I'm leaning more towards the first option, so let me know if you'd really prefer the second