for `read_between_lines` function commands.rb. Removed before/after
hook output text (too spammy). Fixed file-mode completion, so it works
straight away. CHanged 'pry' rake task to 'binding.pry' instead of
just 'pry' so that context is given.
Changed tests to remove opts[:output] and then removed opts[:output]; replaced with output method, changed prompt in example_commands.rb to have a math* wait prompt. Added bullet points to examples in README.markdown. Added more info on TexPlay and Gosu for example_image_edit
* defined input/output accessors for Pry class to set global defaults for input and output (overridable by specific instances).
* Added reset_defaults method to set input/output and prompt lambdas back to defaults
* added output callback for 'cd' command
* changed eval_string += val to eval_string << val in Pry#r method, for performance reasons (no copy made with <<)
John Mair