Add a timedelta validator and checker

[insightindustry]

A bug was reported in SQLAthanor (insightindustry/sqlathanor#80) that occurs when attempting to convert a string measuring an amount of time (rather than a time of day) to an Interval object, which is itself a given number of seconds (a classic Python timedelta representation).

Therefore, there is a need that the Validator Collection support validation of an amount of time, either expressed as a number of seconds or expressed as an amount of time (e.g. '00:35:00.00000') and return a timedelta object.