Suggested Validator: DateTimeRange

[elbenfreund]

Hello Alec,

first of all: thank you for your wonderfull library! 👍

As the maintainer of projecthamster, handling and validating all kinds of time/date/dateime related data is somewhat of a big thing for me. One rather common task is to handle not only individual datetimes but ranges. That is, to make sure that some data

• is actually a range
• and that the range passes basic sanity checks: start < end

Is this something you would be interested in as a PR (same with regards to a validators.Time funciton similar to validators.Date?