Provide [major|religious|national] holiday offsets
#### Motivation

`pandas` does a wonderful job when working with time series - e.g. it is easy to find periodic patterns. There are straight forward methods to find these patterns for standard time intervals such as days, weeks, months and years.

However, it is trickier to find these patterns when they occur in other periodicities or irregular but defined intervals. Often religious holidays depend on the moon or a calendar different from the western calendar ([ISO 8601](https://en.wikipedia.org/wiki/ISO_8601#Usage)). Easter is such an example and already has an offset in `pandas`. It would be very practical to get offsets to other holidays as well, like [iftar](https://en.wikipedia.org/wiki/Iftar), [Chinese New Year](https://en.wikipedia.org/wiki/Chinese_New_Year), [Passover](https://en.wikipedia.org/wiki/Passover), [Krishna Janmashtami](https://en.wikipedia.org/wiki/Krishna_Janmashtami) and [Kanamara Matsuri](https://en.wikipedia.org/wiki/Kanamara_Matsuri) to find patterns relative to their timing.
