[Neutron] NCrystal 2.0.0 release

[Thomas Kittelmann]

Dear all,

A new major release of NCrystal, v2.0.0, has been finalised and released 
at GitHub (https://github.com/mctools/ncrystal/releases/tag/v2.0.0).

The main feature of this release is that it finally brings proper 
state-of-the-art inelastic physics to NCrystal. Modelling of inelastic 
interactions is now always based on scattering kernels, but for 
convenience users need merely provide a phonon Density Of State curve as 
input, and NCrystal will automatically generate the corresponding 
scattering kernel on the fly.

This is of course in addition to the pre-existing features for 
Bragg-diffraction in powders and mosaic single crystals, and also the 
incoherent-elastic component has been improved. NCrystal v2.0.0 thus 
enables realistic thermal neutron interactions in a wide range of 
materials, including now also liquids like water and heavy water. It can 
be used in a wide range of use-cases, including both stand-alone 
C++/C/Python code and to enhance simulations with applications like 
Geant4 or McStas.

We have provided an overview with more details of user-facing changes in 
v2.0.0 on https://github.com/mctools/ncrystal/wiki/Announcement-Release2.0.0

General instructions concerning NCrystal can be found at the wiki page 
(https://github.com/mctools/ncrystal/wiki) or in the NCrystal framework 
paper released with NCrystal-v1.0.0 
(https://doi.org/10.1016/j.cpc.2019.07.015).

We hope you will enjoy this release, and look forward to any feedback!

Best regards,
The NCrystal Developers