ENH: BusinessHour to support multiple opening and closing times per day
BusinessHour supports arbitrary start and end times.  But some businesses open and close more than once per day.  Some examples:

 * Restaurants, who might want to analyze foot traffic or revenue, but excluding times they don't open.
 * Stock markets, several of which have a lunch break.
 * Mexico, where standard business hours are 07:00-14:00 and 16:00-18:00.

Many use cases could be satisfied by just two opens and two closes per day, but it might be just as well to support any amount.