create_diag_indicators: Create IP Diagnosis Indicators
In evanjflack/polypharmacy: Behavioral Hazard and Patient Decision Making

Make indicators for diagnoses in 3 different categories: (1) AMI, (2) stroke,

create_diag_indicators(
  DT,
  DT_id,
  id_var,
  ami_codes,
  stroke_codes,
  diab_codes,
  suicide_codes,
  od_codes,
  od_e_codes
)

`DT`	data.table with ip diagnoses
`DT_id`	data.table with all id_vars
`id_var`	character vecotr with names of coulumns to aggregate on
`ami_codes`	character vector of ami icd9 codes
`stroke_codes`	character vector of stroke icd9 codes
`diab_codes`	character vector of diabetes icd9 codes
`suicide_codes`	character vector of self harm icd9 codes
`od_codes`	character vector for overdose codes (non-e)
`od_e_codes`	character vector for e overdose codes

data.table with id_vars and the following other columns:

`ami`	ami indicator
`stroke`	stroke indicator
`diab`	composite diabetes outcome indicator
`rep_fail`	respiratory failure indicator
`resp_arr`	respiratory arrest
`suicide`	any self harm
`od`	overdose