Resolves #144

[buro9]

This was more complex than I thought... but:

• Have laid the foundation for form input processing
• Have laid the foundation for form validation
• Have laid the foundation for abstraction between forms and models
• Have got the POST working for comment content
• Have got the redirect working across HTTP methods (HTTP 303 is your friend)

End result is that comments can now be created. There's a little cleanup that is possible, and I've left in some GET path redirect handling as /newest is still rendering inline, but this is all good and it works.

[buro9]

@pascalopitz I'm going to merge this so that you can use it...

Note: The HTML form elements are using the same naming and case as the Go models. i.e. ItemID rather than itemId.