Close #86

This updates the docs to ensure that hook parameters exactly match the names
in the code.

Prior to 4.7.19, the names of hook-parameters didn't really matter (as long
as they were in the right order).  In 4.7.19, the names took on extra
significance because Symfony-based listeners use objects and fields (e.g.
`$event->firstParam`) instead of ordered params (`function($firstParam)`).

 * Rewrite "Events"
 * Use more consistent style in the two examples
 * Move some "notes" into new section, "Methods"

What's wrong with a little inversion of logic?

Should use the 'title' property given the example, as the 'name' is the machine name

remove hookref-old.md and move all content into relevant files. Add wordpress setup information for hooks.

- update overview
- add tips and warnings
- add section on hook naming
- replace long code blocks (that focus more on other components) with simpler blocks that show hook usage only
- replace validate with validateForm
 - remove complicated example for setting custom values
 - update tokenValues function to match newer version
 - remove examples of executing raw SQL

This commit mostly adds Markdown tweaks.

I also struck the comparison to pre/post hooks... because I enjoy removing words. 

related to https://issues.civicrm.org/jira/browse/CRM-20187

Fixes #79

fixes #84