Add Tau constant to Math
Today (June 28) is Tau Day! to honor the true circle constant tau = 2*pi = 6.28.
Michael Hartl (https://tauday.com/tau-manifesto) sent out an email today, to,
remind people that it's Tau Day, with the news that Python has now included the
tau constant in its Math Module.
Now we can't let Python have all the fun and beat Ruby!
Please include the tau constant in Ruby's Math Module, to show it's tautally cool too! :)