Extrapolating the bcc address from the envelope

Will create a pull request on Griddler now that has minimal changes and depends on this parser to actually get the bcc. Hopefully this will help.

In response to this: 
https://github.com/thoughtbot/griddler/issues/168
Or:

```ruby
envelope =  json_to_hash(params[:envelope]) || {}
bcc = envelope.fetch("to", [])
```