Add support for Octavian

[kyleaoman]

Apparently Caesar is getting a successor/re-implementation called Octavian. I haven't seen any details yet. @romeeld is there a repo?

[romeeld]

Octavian will probably be ready sometime next year. It should have the same file format as Caesar so I don't think this will require much if any modification to swiftgalaxy. There is a repo but it is not really ready for use.

[kyleaoman]

Thanks Romeel, just wanted a note somewhere to track this for now. Will see whether much needs doing in swiftgalaxy, will depend how similar the python API is to the one for caesar. I rely on the caesar python package to read the files, I don't read them directly. Will wait until that's reasonably settled before integrating it in swiftgalaxy, but feel free to let me know when it gets to that stage if you think of it (or @ me in an issue on that side to track it, whatever works).