Test using Aqua v0.8

[jishnub]

Also, rewrite method signatures to get all the Aqua tests to pass. The idea there is that in the NTuple{N,T} form, T isn't known if N==0. Rewriting this as Tuple{T, Vararg{T}} ensures that T is not ambiguous.

[jverzani]

Thanks. You taught me about Vararg! Any thoughts on the stack overflow that happens with the ImmutablePolynomial type? (I didn't check,but my guess is there is an option to cut out a constructor.) I can pursue if you don't know right away what is up.

[jverzani]

Thanks,I merged this as part of #546. Hope I didn't miss the intent with my modifications. Do let me know if I missed something.