Add tests for elisp and Rakefile to run tests

This PR contains:
  * Tests for Emacs Lisp (requires ERT, built-in since Emacs 24.1)
  * Rakefile to run tests for Ruby and Emacs Lisp
  * Modification of Development section in README.rdoc
  * Removal of unnecessary code in test

It may contains too many changes. Should I split this into smaller PRs?