Return a random element from the range.
(1..4).at_rand #~> 2
(1..4).at_rand #~> 4
(1.5..2.5).at_rand #~> 2.06309842754533
(1.5..2.5).at_rand #~> 1.74976944931541
('a'..'z').at_rand #~> 'q'
('a'..'z').at_rand #~> 'f'
CREDIT: Lavir the Whiolet, Thomas Sawyer