use Ruby's built-in debugger.

* require 'debug' for MRI/JRuby.
* require 'rubinius/debugger' and Rubinius::Debugger.start for Rubinius.
fix Gemfile
replace 'tap' with 'ubertap' to unify methods -- then add in line_no reporting
add 'all' config option for global defaults
replace merge chain with reduce
clean up