Follow-up for the documentation revamp at 38705c4.
- LICENSE -> COPYING: Source files are still pointing COPYING file
- GNU -> GPL: Follows the file name in CRuby distribution
- LEGAL: Recovered from docs/old since it has lib/em/buftok.rb.
lib/em/buftok.rb is covered with exactly the same term as EventMachine
itself so LEGAL file would not be needed (I'm not a lawer!)