simple request tracing

 reqtrace is a package for simple request tracing. It requires nothing of its
 user except:
 .
  * They must use golang.org/x/net/context.
  * They must add a single line to each function they want to be visible in
    traces.
 .
 In particular, reqtrace is console-based and doesn't require an HTTP server.
 .
 Warning: This package is still barebones and in its early days. The author
 reserves the right to make backwards-incompatible changes to its API. But if
 it's useful to you in your current form, have at it.