General code update - add HashPresenter

Hello, I've tried to update a bit the code since it has not been touched for a while, i.e. adding a Gemfile and updating a bit the gemspec.

I also added the HashPresenter class, which is the main reason I'm making this pull request. I needed to access the data received from wolfram in a more convenient way, so I decided that adding a presenter was a good solution. 

I also updated the gem version to 1.3, basically everything is set up for a new release, hope you can build and release it so the updated version will be available directly from rubygems.

Have a nice day

Andrea