* 0.0.5
  - Added `di_ppg_iterate` helper function to iteratively calculate DI across many variables.

* 0.0.4
  - For functions related to the percentage point gap method, add `prop_sub_0` and `prop_sub_1` parameters to account for scenarios where the `proportion` contains 0 or 1 to not lead to a zero MOE when `use_prop_in_moe=TRUE`.  Also, add warning messages when this happens.

* 0.0.3
 - Document definition of `di_indicator` in `di_ppg`
 - Change `pct_hi < reference` to `pct_hi <= reference` in determining DI to be consistent with the methods document from the Chancellor's office
