text: Title: Hard Limit Recursion Limit on `default_calls`
  Body: Is there a specific reason the value `5` was chosen here?
  
  `if self.default_calls > 5` https://github.com/ijl/orjson/blob/master/src/encode.rs#L227
  
  If it's not a hard limit would it be possible to add it as an optional param to `dumps()` to enable the developer to choose what that limit would be?
  
  I am not a Rust developer but I was able to put together a working proof of concept here:
  https://github.com/brianjbuck/orjson/commit/eb9cfb8c7d84c6afd41693e1e310b64b5ea7c0a2
  
  If you wanted to give feedback I can make edits and possibly a PR if you like.
  