Copy-edit

A bunch of minor copy edits have been made to the guides.

I haven't tried fixing the following issues I saw in the past:

* The code starting with "class CommentsController < ApplicationController" has too much indentation, IMO. So do some other code snippets.
* The pink highlighting of the routes file is distracting. Don't know how much work it'd be to fix, though.
* "Finally you should be able to browse to the URL that Heroku has given you and check to see that your blog has been deployed properly!" need to mention when the URL is given. That is, it's the "heroku create" step that does that.

I created a lot of small commits, rather than one large commit, to make it easier to handle any conflicting edits, such as migrating the guide to Rails 4.0. Feel free to squash these commits into a single commit.