Explicit is better than implicit: please don't pull config from the environment

Automatically deducing runtime config from environment variables is textbook spooky-action-at-a-distance, and makes programs that use your middleware less intuitive and harder to reason about. The format of the http.ListenAndServe addr string is time-tested and robust. Better to use it explicitly in your Run method.

Other small fixes:
- package log automatically appends \n to output lines
- Names_With_Underscores are nonidiomatic