Remove unnecessary InstanceMethods module

Stack Overflow has a good explanation of why the InstanceMethods module is
overkill:
http://stackoverflow.com/questions/8706897/why-has-the-instancemethods-module-been-deprecated
Tell people how to install all required gems
Clarify logic around authentication
Merge pull request #5 from gabebw/gbw-remove-unnecessary-module

Remove unnecessary InstanceMethods module
Merge pull request #6 from gabebw/gbw-extract-method

Clarify logic around authentication, and update README re: appraisal install