Change statement to note.

Highlight the fact that extensions to parse should be specified before
connection routes.
Add info about AppView.
Merge pull request #1875 from cakephp/3.0-routes-extension

Change statement to note.
Reduce overly redundant AppView reference
Corrected a to an
Added code-block annotations
Not a function.
Use custom helper instead of HtmlHelper in example.
Fix formatting.
Merge pull request #1877 from cakephp/3.0-app-view

Add info about AppView.