Some more details about creating a settings page for an extension.

Typo

Changed the line numer in the link of the example file for declaring the settings folder.

https://github.com/civicrm/civicrm-dev-docs/pull/425#issuecomment-338253390

related:
https://github.com/civicrm/civicrm-user-guide/pull/232

Resolve #316

Specifically:

 * Alphabetize
 * Add general description

Not sure of the Petition Signature Pages URL - its not Event registration....

Replace 'Wordpress' with 'WordPress' to use correct camel casing according to the WordPress Wordmark and Trademark

Update framework/setting with updated link for settings override and also add in notes in regards to group_name now being domain or contact in 4.7 and update example

Fixed typo: transacftion, now: transaction

**N** does not render as bold in the code text, so replace with easier read IDNUMBER.
Fix incorrect >**N** in some URLs.