added new features including creation of temporary tables using aou_compute() and aou_create_temp_table() and a new aou_collect() function which accomodates bit64 integers when needed.
simplified aou_observation_period() function to look at earliest and latest clinical events rather than strictly implementing OHDSI conventions per expert advice
all functions with the option to collect data locally default to collect = FALSE
minor big fixes, improved error messages, and improved documentation