Add KernelSpecManager.get_all_specs

[captainsafia]

Closes #66.

cc/ @minrk @Carreau

[jankatins]

This is IMO misnamed, at least I have trouble seeing this NOT as a function, which gets a helper object, but it returns a kernel spec as far as I see it. So _get_kernel_spec_for_name(name, dir) or _make_kernel_spec(...)?

[captainsafia]

I concur with what you say, @JanSchulz. Let me update the code.

[jankatins]

Does this also need a change in the notebook to take advantage of this new thing? [Edit: yes, it also iterates over all kernels: https://github.com/jupyter/notebook/blob/master/notebook/services/kernelspecs/handlers.py#L56]

[captainsafia]

Noted, not sure if it'll be include in the 4.1 release but I don't see any reason as to why it shouldn't.

[minrk]

let's call this get_all_specs. That way get_ returns kernelspec objects, while find_ returns locations on disk.

And don't forget to add a docstring.

[minrk]

Thanks!

[minrk]

@captainsafia feel free to ping with a comment when you've addressed notes, so we can review/merge; we don't get notified of new commits, only comments.

Thanks again, this is great!

[captainsafia]

Yep! For some strange reason, I thought i had more work to do on this before it was merge ready but if it looks good, sweet!

[captainsafia]

I remember it now. Had to rename the test_find_all_specs to test_get_all_specs but I don't think that's too big a deal.