Updating the Getting Started guide's documentation

[natechicago]

This pull request contains a number of individual changes, but they all fall into a few common categories:

• Correcting minor mistakes which, in aggregate, make this document a little more difficult to read than it could otherwise be. These include misspellings, improper casing, grammatical inaccuracies, and run-on sentences.
• Revising statements/claims that were either accurate at one point but are no longer, or whose imprecise wording leads to unnecessary ambiguity and confusion.
• Reorganizing a few sections so that terms (like "owning" side vs. "inverse" side) are defined before we assume the reader knows what they mean, and concepts (like Unit of Work) are introduced when they are immediately supported by the neighboring code.
• Ensuring the sample code is consistent throughout the guide (eg. a property defined initially as 'protected' shouldn't show up as 'private' further down in the guide).
• Adding entity type hints to setter methods to make the code more expressive.

In its current state, Doctrine's documentation is already quite fantastic. Yet it could still benefit from a little extra polish. I strongly believe that the modifications contained herein will significantly improve the accuracy and readability of the Getting Started guide. This is obviously an important goal, since the Guide is likely the very first point of contact that many new users will have with Doctrine.

[natechicago]

The statement "Now that we have defined the Metadata mappings" is not accurate. At this point in the tutorial, we haven't defined any metadata mappings yet.

[natechicago]

This section regarding ArrayCollection seemed to be incorrect, since no objects of type "Doctrine" are involved here. Please confirm the accuracy of the re-write, though.

[natechicago]

@Ocramius is there any appetite for these types of changes from the core Doctrine team? I have some improvements to offer for other sections of the tutorial too, but would like some feedback on this one before submitting them.

[Ocramius]

@Ocramius is there any appetite for these types of changes from the core Doctrine team?

There is, but I really didn't manage to track this one before today, sorry :-(

Keep 'em coming! I'm merging this one after a manual rebase :-)

Thanks for your help!

[Ocramius]

Manually merged via b925cce