The majority of the data is exposed via the environment and the actual body is
piped to the script. This change allows for a great deal of flexibility with
regards to templating---users may write "templates" in whatever language they
choose to generate whatever output they wish.
We should do as much processing beforehand as possible so that the template does
not need to, for example, start snooping through the repos (which will be more
complicated once we support multiple VCSs).
Mike Gerwitz