Nonlinear Axes in DataND

[trisyoungs]

Describe the feature / issue
Our DataND classes have axes which are:

• Often assumed to have a regular stepsize between points
• Not regulated in any way.

At some point we will need to allow for logarithmic axes (e.g. for coarse grained simulations). We may wish to consider making a specific DataAxis class which contains the axis values but also the limits, stepsize, increment, logarithmic step etc. used to create it in the first place. This would allow us to perform checks when manipulating datasets - adding, subtracting, averaging etc. - to see if the axes match and straight arithmetic operation can be performed, or if interpolation is required to do so. At present, there are an increasing number of assumptions that this is the case in the code.