Version associated with PLATON II paper (final)

This is the PLATON release that corresponds to the final version of the second PLATON paper (https://arxiv.org/abs/2004.09513).

Improvements:

1. Example files are a lot better
2. final evidence is made more explicit, stored in final_logz of the RetrievalResult object
3. eclipse_depth_calculator now uses Simpson's rule instead of Trapezoid rule, which improves accuracy by ~1%
4. Collisional data initialized in constructor, which speeds up R=10,000 calculations
5. Added warnings for when the user species bins that are too small, or tries to use high resolution opacities without specifying that the star is a blackbody
6. The radiative transfer calculation for emission is now reformulated to use E3 instead of E2, which guarantees exactly the right result for an isothermal atmosphere, and better error properties for near-isothermal atmospheres.

Bug fixes:

1. RetrievalResult plot_specturm now handles correlated k results properly
2. For correlated k, unbinned_wavelengths, unbinned_depths, etc now work properly

The attached zip file is the data directory associated with these release. It should not be necessary because PLATON automatically downloads the data from a server. We upload it here in case the server ever goes down.