Extension methods for the DiscreteTime.
| Abs | Returns the absolute value of a time value. | 
| Clamp | Clamps the value x into the interval [a, b]. | 
| Floor | The lower integer number of seconds represented as a DiscreteTime. | 
| Max | Returns the maximum of two time values. | 
| Min | Returns the minimum of two time values. | 
| Select | Returns b if c is true, a otherwise. |