Get access to response object easily.

[chitgoks]

Feature request

Glide Version: 4.13.1

Not much other detail to provide. just that it would be nice to have an easy way to get access to the response object, specifically the response header.

[halizton]

+1 to this use case, we pass some CDN cache hit/miss information as response headers to the client for each image loading, it would be great if we can expose the response headers via the RequestListener interface. Lower level network libraries such as okhttp or cronet does have response headers exposed.