Changed copyright end year to 2020 in every reference "Copyright (c) 2006-XXXX, assimp team".
Changed copyright end year to 2020 in every reference "Copyright (c) 2006-XXXX, ASSIMP Development Team".
Changed copyright end year to 2020 in LICENCE.rtf.
Changed copyright end year in CMakeFiles.txt files and any other places referencing Assimp with a copyright start and end year.
This also fixes issue with root bone overwritten - which should not happen as it is a hack.
Before the behaviour would create an additional bone which would end up breaking animations completely on import.
Additionally this fixes required bones being removed.
Co-authored-by: K. S. Ernest (iFire) Lee <ernest.lee@chibifire.com>