Fix Spelling and Grammar errors.

- Fix one spelling error and one grammar error on Installation
- Add 'so' to clarify the meaning of the first bullet on Preparing Your
  Application
- Fix two spelling errors, add missing words, and change authorize to
  authorise for normalization on Preparing Your Application
- Fix spelling errors on Authentication & Authorisation
- Fix spelling errors in Cold Start

I did not regenerate the compiled html due to an issue I had with pushing the blog post back a day (e.g. 2013-06-01 became 2013-05-31).