Return same table type as passed in predict

[andreasnoack]

Opening a separate issue for this such that we can make a decision before cutting a 2.0 release. See also prior discussion #174 (comment). Right now

data = DataFrame(X=[1,2,3], Y=[2,4,7])

OLS = glm(@formula(Y ~ X), data, Normal(), IdentityLink())

newX = DataFrame(X=[2,3,4])

predict(OLS, newX; interval = :confidence)

returns a NamedTuple. It might be possible to generically return the same table type as passed.

cc @nalimilan