Use dims keyword to identify axis to use

[rofinn]

For HoD, Periodic, OneHotEncoding we should be able to reuse the dims keyword to apply the transformation to the axis values. I don't think the user should explicitly need to do KeyedArray(Periodic(sin, Day(1))(a.time); time=a.time) just to get a KeyedVector back with the original time axis.

[glennmoy]

This feels like it would be an inconsistent use of dims compared to the rest of the package, which uses it as an arg in selectdim. But I'm sure we can do something about it.

Also, just leaving this as reference for now as there may be further relevant conversation here:
#62