Builds shares of renter households who pay more than 30 or 50 percent of their income in rent and the average median rent burden (rent / household income) in the CoC.
build_coc_rent_burden(year, tract_crosswalk)| tract_crosswalk | A data frame with a census tract to CoC crosswalk from
  | 
    
|---|---|
| yr | A numeric with the year of the data.  | 
    
A data frame:
coc_number: CoC number (character)
year: Year (numeric)
share_rent_over_30_pct_inc: Share of renter households paying more than
30 percent of their income in rent (numeric)
share_rent_over_50_pct_inc: Share of renter households paying more than
50 percent of their income in rent (numeric)
median_rent_burden: Median rent share of income in the CoC (numeric)