Utilization pre/post SQL queries

[KevinKloiber]

Prior and post-discharge utilization might be helpful or interesting for researchers and their studies.

While the inpatient count is pretty straightforward, it should be noted that ED visits can only be identified using the transfer table, since the ED table was only included in later years and does thus not account for ED visits that occurred in early years (anchor_year_group 2008-2010). So simply using the ED table that is provided by MIMIC might lead to a miscalculation of utilization, especially in prior years. I also added two post-discharge variables that separate ED visits by ED visits with admission and without admission.