Returns a randomly generated number.
rand 10 # returns an integer i, 0 <= i < 10
rand 10.0 # returns a float f, 0.0 <= f < 10.0
rand 1 11 # returns an integer i, 1 <= i < 11
rand 1.0 11 # returns a float f, 1.0 <= f < 11.0
rand 1 11.0 # returns a float f, 1.0 <= f < 11.0
rand 1.0 11.0 # returns a float f, 1.0 <= f < 11.0
When give no argument, it simply takes the current payload['ret']
sequence
10
rand # returns an integer i, 0 <= i < 10