It's absolutely irrelevant for the client and request/response packages should
only contain code that is useful on both sides of the conversation. It's OK
for client tests to reuse this code, but the package is used by external
developers and they shouldn't be bothered with it. Nothing changed
functionally here except WSClient simplification. Fixes#2236.
It's not needed any more with Go 1.13 as we have wrapping/unwrapping in base
packages. All errors.Wrap calls are replaced with fmt.Errorf, some strings are
improved along the way.
Mostly as is, no real effort done yet to optimize them, so there are still a
lot of duplicates there, but at least we sort them out into different smaller
packages.
