Added .gitignore file
Updated Gemfile: incorporating all gems and adding pry-debugger
Fixed up spec_helper. Now does smart $LOAD_PATH adding so all files are easily accessible. Also requires pry so it's available for all specs
All required models required via single support helper (for integration specs)
Redid directory structure:

* All application code under app/
* Domain objects under app/domain
* Folder names all lowercase
* Also added InitializationError class to Cargo and Delivery
Moved integration specs to spec/integration/*
Cleaned up the cargo_repository_spec and added stubs to remove Mongo dependency
Added isolated tests (unit tests):

* Every domain class has a single unit test spec
* directory structure is parallel: spec/domain/cargo/cargo_spec.rb => app/domain/cargo/cargo.rb
* Implemented full unit tests for Cargo
* Implemented full unit tests for Delivery
* placeholders for other specs
Moved app/domain and app/ports to top level. Ditching 'app' to make domain more prominent. Also updated specs a bit more.
Added Value Object baseclass and tests
Merge branch 'dans_spec_work' of https://github.com/drsharp/ddd_sample_app_ruby into drsharp-dans_spec_work