Spectra.jl Across the Electromagnetic Spectrum

Spectra.jl already handles UV, optical, and IR spectra, but has no capability for loading spectra like X-ray and gamma-ray, as they are different from UV/optical/IR spectra. X-ray astronomy (and other high energy fields) typically operates on spectra that are binned into channels by the measurement device. An instrument response matrix (RMF) is required to map detector channels to physical energies, and an ancillary response file (ARF) provides the telescope's effective collecting area, and both are needed to correctly convert raw channel counts into physical flux. SpectralFitting.jl already contains an OGIP parser that handles these formats. It has been agreed upon that the correct long-term architecture is for the spectral types to live in Spectra.jl, with SpectralFitting.jl eventually depending on Spectra.jl rather than duplicating data structures. Beyond data loading, observers also need a standard set of tools before any science can be done, such as rebinning according to different heuristics, adjusting the wavelength or energy shifts, or converting between common units. This project implements those tools in Spectra.jl as well, making it easier for users of Spectra.jl.