given a dataframe look through and calculate the doubling times. Both doubling time based
on the first occurance of covid-19 and doubling time based on a rolling window which
looks back as far as the median incubation period (converted to integer using ceiling)
Parameters:
df: pd.DataFrame
the dataframe containing the region data
col_suffix:str
cumulative column suffix used to filter the dataframe to only grab cumulative data
uses pd.DataFrame.filter(like=col_suffix)
combine_df:bool
if True will return a new dataframe with the doubling time data joined with the old dataframe
if False will only return a dataframe with the doubling time data