Added a summary method for class gComp objects
Added additional error checks for the the new summary and print methods
Added functionality to use negative binomial distribution for overdispersed count/rate outcomes with outcome.type = "count_nb" or outcome.type = "rate_nb".
Changed order of operations for calculating risk difference which resulted in changes to previous estimates at the hundredths decimal place.
Added additional error checks to prevent users from inputting incorrect data structures.
Added a NEWS.md file to track changes to the package
Updated vignette titles to be more descriptive.