[FR]Axis scale option 1/x

[jonschlipf]

Hi,

For a type of plot I will be doing quite often in the near future, it would be very helpful to have a secondary x axis on top of the plot featuring "inverse" (1/x) tick scaling. Basically like this stack overflow discusstion for the case of Python.

https://stackoverflow.com/questions/56418477/displaying-wavenumber-and-wavelength-on-one-plot
This coule be achieved easily via twiny(), if there was an option :inverse for the axis scale. Currently available are only:
[:identity, :ln, :log2, :log10, :asinh, :sqrt]

Since Plots.jl is a "meta" package, at this point I do not quite understand if this would have to be done in Plots itself, or at the interfaces to all backends. I would appreciate if someone could implement this if it is not too much effort, or point me to what I would have to modify to do it myself.

Cheers