feat: add WhoisContext and use context for all queries

[babariviere]

Close #39

This implementation will keep the same implementation as before.

There is only one breaking change if someone was calling client.SetDialer which now requires a dialer with a context.

[babariviere]

@likexian If you want me to preserve the SetDialer API, I can wrap the dialer without context in a dialer that ignore the context but I don't think that's a good idea and I don't know of a better one.