Preserve leading underscores for camel_case_key

[smdern]

Elixir's Macro.camelize will ditch any leading underscores and upcase
the first letter.

e.g.

iex(4)> Macro.camelize("_foo")
=> "Foo"

[johnnyji]

@smdern

Thanks for the discovery and contribution!

[smdern]

@smdern

Thanks for the discovery and contribution!

Np. That was fast. I created a plug that transforms incoming requests and the responses if you're interested, I can contribute that as well..

an example usage

plug TransformParams,
  params: &ProperCase.to_snake_case/1,
  response: [
    json: &ProperCase.to_camel_case/1,
    plain_text: &String.upcase/1,
  ]