Support `res.setEncoding` and non-text response types

Response data in http-browserify seems to default to text. In node http it seems to default to buffer. Independent of defaults, the node version supports `setEncoding` so you can change the type of the response. The browserify version should do the same.

The issue names no file, test, or entry point, so first locate the response implementation and existing handling of response data. Compare its behavior with Node's http response and determine how setEncoding and non-text response types should work; done means the browser implementation supports setEncoding with matching response data behavior and tests cover it.

Written by the indexing model from the issue text.