Add Gemfile
Make file executable
Add shebang line
width and height are "read-only"

Also, eschew the uses of instance variables to make it
easier to DRY up later
Use RSpec
Add first spec

Fix invocation of Fixnum#between?
Add .travis.yml
Merge pull request #1 from BanzaiMan/master

Add Gemfile and a bunch of other stuff. Thanks again Hiro!