mctools/ncrystal: NCrystal release 3.0.0

After almost a year of intense work, the NCrystal developers are very proud and excited to finally being able to present the NCrystal v3.0.0 release!

Most importantly, this release brings support for multiphase materials, material density control, SANS physics, goodies for McStas users, and various smaller but hopefully useful new features such as defining simple unstructured materials without the need for data files, new handy cfg-parameters, and other quality-of-life improvements. In addition, the release brings many other new features and technical improvements "under the hood", with around 19.000 lines of code changed in more than 300 files!

Please refer to the release 3.0.0 announcement page on our wiki for a slightly more detailed overview about this new release! Furthermore, we would like to encourage users to post questions concerning the new release (or anything else NCrystal related obviously) to the forum.