Update to CoffeeScript 1.7.0
Use true mathematical modulo operator '%%' for wrapping slot index, replaces properModulo()

CoffeeScript 1.7.0 worth it just for this operator, a modulo
that works the way you would expect (-3%%2=+1, not -3%2=-1)

References:
https://news.ycombinator.com/item?id=7139175
https://gist.github.com/aseemk/8637896