Should `unflatten` unwrap `Fixed` values?

I am finally getting around to #30. In doing so I noticed:

julia> x = (1, 2.0, fixed(3.0))
(1, 2.0, ParameterHandling.Fixed{Float64}(3.0))

julia> v, unflatten = flatten(x);

julia> unflatten(v)
(1, 2.0, ParameterHandling.Fixed{Float64}(3.0))

Since wrapping something in Fixed is only done for the sake of the flatten/unflatten machinery, I wonder if it would be better for unflatten to return the unwrapped value of the Fixed number, since that's all end users will generally care about. Or I guess another question to ask is: Are there any situations where the end user would want the Fixed-wrapped value rather than just the value itself?

Start by reading issue #30 and the three comments on this issue, then reproduce the Julia REPL example with flatten and unflatten. Determine whether unflatten should preserve Fixed wrappers or return their values; done requires a decided behavior and corresponding validation.