CRM-20332: modify summaryAction hook to allow user-defined action in third column of action list

Correct typo - missing comma

Update docs home page URL

Update hook_civicrm_dupeQuery.md

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

by passing custom options to the pygments PHP lexer, now that this is
possbile with pymdown-extensions 2.0

Per request from Josh, this needs to be changed ASAP.
We will find a better name at some point soon.

WIP How to document your extension

This book isn't published yet, but I want to get this page up
and running. Will uncomment when CiviVolunteer books is up.

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

Commit for issue #104

Added a requirement for community and official ext

Fix typo in hook_civicrm_angularModules.md

Update hooks page

- 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

Update documentation.md