identifypd: Extract lastest period of dataset
In ICPI/ICPIutilities: Utility functions for working with or creating ICPI products

This function is pulled from the achafetz/PartnerProgress repo

1	identifypd(df, pd_type = "full", pd_prior = FALSE)

`df`	dataset to use to find latest period
`pd_type`	what is returned? (a) full, eg fy2018q1; (b)year, eg 2018; (c) quarter, eg 1
`pd_prior`	do you want the last period returned (instead of the current); default = FALSE

## Not run: 
#return full, current period, eg "fy2018q3"
identifypd(df_mer)
#return the current quarter, eg 3
identifypd(df_mer, "quarter")
#return the prior quarter, eg "fy2018q2"
identifypd(df_mer, pd_prior = TRUE)
  
## End(Not run)