Implement GetAllAsync so we can inspect the status code

[shiftkey]

Some parts of the API should show a specific error message when you:

• interact with an API that uses a GetAll
• the status code returned when the input cannot be found is 404
• we should handle this and return a human-friendly error message

Relates to #238

[hnrkndrssn]

Let's see if I have understood this one correctly...

For example in the ReferencesClient we have GetAll and GetAllForSubNamespace, which call ApiConnection.GetAll<>.
Now, instead of calling ApiConnection.GetAll<> we'll create a new GetAllAsync<> on ApiConnection which will, in addition to what the existing call to ApiConnection.GetPage<> does, BUT also check the HttpStatusCode of the response and if it's a 404 return a human friendly error message?

And this should be done for all the GetAll type methods?

[shiftkey]

It's kinda fiddly, which is why I put it aside but here's the abridged version:

• internally, ApiConnection.GetAll<T> just calls ApiPagination.GetAllPages

octokit.net/Octokit/Http/ApiConnection.cs

Line 112 in bc82697

return _pagination.GetAllPages(async () => await GetPage<T>(uri, parameters, accepts)

• ApiPagination.GetAllPages will enumerate all pages and likely return an empty collection

Perhaps we should have a consistent response inside ApiPagination.GetAllPages when you get a 404

The example I'd like to get passing as part of this is #242 - because when you specify a namespace that is not valid, you should get a specific error message rather than an empty collection.

https://github.com/octokit/octokit.net/blob/master/Octokit.Tests.Integration/Clients/ReferencesClientTests.cs#L66

[hnrkndrssn]

OK, I'll see if I can come up with some ingenious solution to said problem 😆

[hnrkndrssn]

We could pass in the URI being called to the ApiPagination.GetAllPages and in the event of a 404, we return a NotFoundException with an error message of _[URI] was not found._?

That would at least inform the user specifically what was not found, instead of just _Not Found_.

New signature of ApiPagination.GetAllPages would be:

GetAllPages<T>(Func<Task<IReadOnlyPagedCollection<T>>> getFirstPage, Uri uri)

So the example test for #242 would look like:

[IntegrationTest]
public async Task CanGetErrorForInvalidNamespace()
{
    var owner = "octokit";
    var repo = "octokit.net";
    var subNamespace = "666";

    var result = await AssertEx.Throws<NotFoundException>(
        async () => { await _fixture.GetAllForSubNamespace(owner, repo, subNamespace); });
    Assert.Equal(string.Format("{0} was not found.", ApiUrls.Reference(owner, repo, subNamespace)), result.Message);
}

Happy to discuss, I have made changes locally with the above scenario in mind, I can send it through PR for review if you like.

[shiftkey]

@alfhenrik I like it