Bump copyright notice to 2015

The following script makes it a no-brainer:
% NEXT_YEAR=2015; ag -l 'Copyright.*Wiegley' \
  | xargs sed -i '' -e "s/\(Copyright.*\)-20[0-9]\{2\}/\1-${NEXT_YEAR}/"
Use same license text formatting in source files
Merge pull request #355 from afh/pull/copyright

Update copyright