Add four Github badges: (rubygems, travis, gemnasium, codeclimate)

These are arguably the most four important/useful Github badges:
  1. Rubygems (shows and links to latest gem version)
  2. Travis CI (shows and links to status of latest build)
  3. Gemnasium (shows and links to status of dependencies)
  4. Code Climate (shows and links to analysis of code quality metrics)

Together, these are useful tools as well as indicators of the overall
health of the project.

NOTE: You will need to quickly activate the *free* support level for Gemnasium and Code Climate:
 *  https://gemnasium.com/users/sign_up
 *  https://codeclimate.com/signup/account