Edit dependencies in Rakefile and generate gemspec

* Added Rake as development dependency
* Changed Rspec version to use pessimistic operator as suggested in:
  http://guides.rubygems.org/patterns/#declaring_dependencies
* Added Jeweler as a development dependency
* Ran `rake gemspec` to generate new gemspec file
Add Gemfile and ignore Gemfile.lock
Merge pull request #1 from ericmathison/dev-test-dependencies

Specifying Development Dependency Versions