mctools/ncrystal: NCrystal release 2.3.0

For most users this release is identical in features and capabilities to release 2.2.2. The main change is that the NCrystal license conditions are cleaned up, due to a complete rewrite of the internals of the file NCSpan.hh. This file previously contained third party code which was using a different open source license than the rest of NCrystal. With this release, all core NCrystal code is once again cleanly available under the Apache 2.0 License.

The release also contain a few minor technical fixes, mostly related to plugin development. As always, the CHANGELOG contains more details.