Proposal: add scaled TimeValue axes

[mpilgrem]

Module Graphics.Rendering.Chart.Axis.Floating exports scaledAxis but there is no corresponding function exported by module Graphics.Rendering.Chart.Axis.Time.

I found myself needing to specify bounds when creating area spots charts, including charts with TimeValue axes. I have done that in a fork, with additions to the API. Would that be of interest? If yes, I'll make a pull request.

I export scaledTimeValueAxis and autoScaledTimeValueAxis, each like their corresponding unscaled version but with an additional argument of type (t, t).