Build in support for easily creating LUTs

[robintw]

Lookup Tables (LUTs) are really useful for various applications where Py6S simulations are run many times - they can speed up things like atmospheric correction to make them actually possible!

I have preliminary versions of this running as part of my PhD, and will be hopefully releasing them as part of Py6S in the future.

[betatim]

Not sure if you are still working on this or not. I can offer some coding skills, time and motivation (but no real remote sensing knowledge yet) to make this happen. Interested in using this for https://github.com/wildtreetech/sentinel2-bot

[samsammurphy]

I put together a repo that uses Py6S to create look-up tables. My coding skills are fairly modest (I am more of a remote sensing guy) might make for a good starting point @betatim @robintw