accurately returns C source for immediate value instance methods.
* refactored repl into 2 help methods: repl_prologue, repl_epilogue
* added session_target method to Pry instances so can retrieve target
of session for parents, e.g _pry_.parent.session_target
* refactored ls command to use Symbol#to_proc
* Added alias_command and desc commands to Pry::CommandBase
* Added pry and version tasks to Rakefile to start a pry session and show current version
* Added tests for alias_command and desc commands
* made it so ls_methods and ls_imethods return sort arrays
* made it so show_method without a paramater displays current method, if exists, who displays error if not
* Made is to 'def meth;end' in an object (not a class) defines singleton methods, not methods on the class.
* Reorganized and reworded some documentation, adding info on rubygems-test
* added rubygems-test support
* added more tests to reflect new method definition behaviour
