motivation: the Swift Server Workgroup is not a legal entity and cannot hold copyrights. with this change, code authors continue and retain their copyrights under the apache license and previous copyrights note, but Apple steps up instead of the workgroup which has no legal status
changes:
* update header files to say "Apple Inc. and the AsyncHTTPClient project authors" instead of "Swift Server Workgroup and the AsyncHTTPClient project authors"
* update validation scripts to check for the correct header
* add CONTRIBUTING.md file to explain how to make contributions and include a legal notice about licensing the contribution to Apple and the project
* regenerate CONTRIBUTORS.md to reflect most recent contributions
Artem Redkin
tomer doron
vkill