Use REUSE to apply licenses
Currently the license headers in source files are quite big, it takes approximately 20 lines in each file. With REUSE it takes less lines, and with REUSE there are convenient tools to check if all files in a project have a license.
Tools that I've developed and that can be used to convert the license headers:
(gcu-multi-line-substitution and gcu-smart-c-comment-substitution)