including tracefunction in stored comps

[tcrundall]

With the introduction of multiple (i.e. 2) different orbit tracing functions with slightly different results, it is maybe important to store with a component which function was used to fit it.

[tcrundall]

For including the tracing method into the raw stored components this might be tricky encoding that information into an array.

Maybe the components should start being stored as fits files by default, and that way the trace function can be included in as a string. For backwards compatibility when loading a component from a file it can first try the fits file, then if it’s missing do the numpy file and assume (probably) the epicyclic function.