Switch gemspec to Bundler's default format
Provide programmatic access to the version number

Fixes #1
Don't commit Gemfile.lock

See: http://yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/
Add access to bundler's helpful tasks
Don't show a description for the default task when listing tasks
Merge pull request #12 from henare/version

Fixes #1