List of existing implemenations

[mj-will]

This is a follow on from #796.

So far, it seems like there are few different implementations. In no particular order, here are the ones I have links to:

• Version by @narolaharsh and others: https://github.com/lemnis12/relativebilbying
• Version by Ish Gupta - missing link
• Version by @noahewolfe

It would be good to try and restart the discussion on this.

[corvus314]

Implementation by @narolaharsh is waveform specific. It was constructed for PhenomXPHM as it had to reimplement parts of the waveform generation outside of lalsimulation. Not sure if other implementations are more general.

[narolaharsh]

Right, the implementation inside relativebilbying is only for PhenomXPHM. I am a bit busy completing the analysis for the upcoming TGR paper but after that, I'd be happy to put together a merger request for this or work with others.

[adivijaykumar]

Tagging Ish (@img5156) on this issue as well.