Added code to datediff to get unique events if there are multiple concurrent events (such as two medication administrations) at once
Fixed errors when events that have the same times are passed in, and simplified >2 event handling
Merge pull request #3 from projecttacoma/multiple_concurrent_events

Added code to datediff to get unique events if there are multiple concur...
Merge mwptrsn's overlaps with null end dates