Expose Usage Limit Headers as part of responses

[andrewmunn]

Is your feature request related to a problem? Please describe. I want to implement a metric to monitor our usage of PDL and ensure we do not run out of usage credits. Your API requests return your remaining credits as response headers. However, as far as I can tell, there is no way to access the response headers when using this JS client.

Describe the solution you'd like I'd like the usage headers to be exposed as part of the response.

Describe alternatives you've considered I'm considering not using this client (or copying it) and implementing the API myself to get around this.