improve data munging

[megbedell]

Currently there's a high barrier to entry in terms of turning a user's spectral data into the format wobble expects. This could be solved by some combination of the following, unclear which is best:

• simplifying and condensing the existing data munging scripts (so that the user can more easily write their own following that template)
• including data munging functionality within the wobble.Data object class
• requiring that the user load up & pass the relevant data as parameters to initialize the wobble.Data object (rather than silently reading in from HDF5)