Add IsDST() function to AF Analytics

Idea created by Steve.Buckley on Jun 1, 2017

    Originally posted on UserVoice
    Use Case: calculating which Shift is working within a rotating-shift cycle, which must the follow Daylight Savings Time offset.

    This function is available in the Performance Equation library, but not in AF. The function itself is simple once one knows it, but is not obvious (kudos to Nicola Gargano):

    IsDst = Floor(Float('*'-'1-jan') / 3600) Mod 24 <> Hour('*')

    It should be added to the AF function library.

    For more background, see this link: