- Globally change 'Shipping' to 'Shipment' - shipment is a noun and thus a clearer name for an object.
- Add definition of unidirectional to the top of the document.
- Explain inversedBy and mappedBy the first time they are used.
- Clarify some ownership and bidirectionality text.
- Minor English and punctuation fixes.
Added pointers on how to interpret the method names. This helped me to quicker grasp the concept of the Relations and there methods. Added a @var annotation to the `Collection` interface to make it clear that the `$groups` is a child of the `Collection` interface.
