Add support for multiple values on lower intervals

[Mike Cooper]

Currently, no support for rules that have multiple values in lower intervals, e.g.
FREQ=WEEKLY;BYDAY=WE,SA

Need to reprogram the logic to check for multiple instances of lower intervals.

[Shimon Doodkin]

I have developed a minimall algorithm and implemented it in byDay

shimondoodkin@9b56b51

pull it for your self if you like my changes