some makeup on IEx.Debugger pattern-based tracing

* added :debug to IEx.Options[:colors], defaulting to 'cyan'.
* IEx.Server.io_debug outputs debug messages.
Expressions sent to Debugger controller have values

* anon functions are the only corner case, thus those are replaced
  by their original counterparts using Runner.fn_from_second/2
* allows users to inspect values using pattern-based debugging.