Checked 1st half - improved grammar and made code snippets consistent with phalcon/invo code

The tutorial didn't fully match the latest code I downloaded (23-Oct-13 / 001fba25ec59fe801b17d64500d70369cb4c073c) so I've made the tutorial words and code snippets consistent with the latest code.

One issue I haven't dealt with is that a file is referenced which doesn't exist in the latest code: app/views/session/index.phtml

The tutorial code snippet appears to be a simplified version of a file that presumably no longer exists. Instead a more complicated index.volt template file exists which houses the login form. I guess a brief intro to the Volt Template Engine would need to preface a code snippet.