Flux-preserving resampling

[icweaver]

Might be nice to have after #26 is in. Not blocking for registration

Prior art: https://github.com/Michael-Reefe/SpectralResampling.jl

[cgarling]

I would consider upstreaming this to another package (DataInterpolations.jl)? This package's scope is astro but there may be other applications for which it would be useful to have this implementation.

[icweaver]

That's a good point. Speaking of scope... any package name ideas for the rename here? 😅