Merge pull request #8 from rweng/master

CGI::encode broke real requests
add osx deps to gemfile
improve guardfile so that if a file changes, the spec is run
add pry for easy debugging
add fixture_as_json and configure rspec
format post.json
major refactoring, structuring all models under a models module
Remove api.rb and helpers.rb

The modules are quite small and are only used in the client. It is to question whether we really need a separate file. I am not totally against it, but we need to bring some structure in this repository.
refactor Client.contacts to return an array of Models::User
client#contacts can accept an array and string for user_fields