v0.10.0

1. Adds helper methods to support webhook signature verification:

   event = lithic.webhooks.unwrap(body, headers, secret)
   
   lithic.webhooks.verify_signature(body, headers, secret) # throws if invalid.

2. Adds mcc to transactions.
3. Improves handling of union types and coercing potentially incorrect types.

Full Changelog: v0.9.0...v0.10.0