Handling Github webhooks with ChiselStrike and Kafka

[penberg]

This adds an example application for handling Github webhooks with
ChiselStrike and Kafka.

Note! This depends an API that only exists in a development version of
ChiselStrike. If you want to try out this example, please build the
runtime from sources.

Roadmap:

• @barbieri suggested eslint rules and, for example, "event["repository"]["full_name"] could be event.repository.full_name"
• @barbieri suggested "Maybe add a comment why not writing directly to the DB in the endpoint and in the event processing another like “you may do some slow operation, or operation that can crash. If it crashes the event will be reprocessed”