Replace references to GNU Public License to Apache license in:
- COPYING file
- README
- all source code below falco
- rules files
- rules and code below test directory
- code below falco directory
- entrypoint for docker containers (but not the Dockerfiles)
I didn't generally add copyright notices to all the examples files, as
they aren't core falco. If they did refer to the gpl I changed them to
apache.
