implemented method mutate and using it in methods iszero and isinf; renamed method isvalid to isfinite; implemented methods rand and duration2num (the latter is only an alias, since it does the same as num2duration).
implemented method mutate and using it in methods iszero and isinf; renamed method isvalid to isfinite; implemented methods rand and duration2num (the latter is only an alias, since it does the same as num2duration).

jgte/orb,jgte/orb,jgte/orb,jgte/orb,jgte/orb