* Add support for unix socket as upstream
* Add CHANGELOG.md entry
* Add Unix socket documentation
* Don't export unixRoundTripper, switch from string prefix to Scheme match
* Add basic unix server mock
* Add some tests and comments
* Use a specialized ResponseWriter in middleware
* Track User & Upstream in RequestScope
* Wrap responses in our custom ResponseWriter
* Add tests for logging middleware
* Inject upstream metadata into request scope
* Use custom ResponseWriter only in logging middleware
* Assume RequestScope is never nil