Lpipe

- Print exception class dynamically when catching TypeError.

- Pass entire payload via event rather than just the event_source_arn.

- `utils.get_nested()` now has the option of setting a default value, and it will raise a KeyError if the requested keys don't exist.
- Unhandled exceptions will now be raised if debug is true.
- Move event and context into a single dict pased to functions as kwarg `event`.
- Pass event source ARN to Payload and, subsequently, to the event dict passed into functions.

- Add ability to pass kwargs even if they aren't in the signature

- Refactor most tests to just use moto.
- Add s3 testing helpers

- Backfill CHANGELOG
- Pass event and context to every function