Add hook_civicrm_findDuplicates documentation

Add explanation about interactive rebasing

Update hook_civicrm_permission_check.md

Formatting tweak

Add note about custom data on any creation

Resolve #577 Fix URL pointing to how to set up extension directory

Add in notes about support for KeyColumn parameter when using option …

Added additional headings to facilitate more precise linking

Fix bad link/duplicate text.

Add missing variables to hook_civicrm_export

Add in notes about support for KeyColumn parameter when using option group as part of a setting pseudoconstant

Fleshed out validate_callback doc.

Describe new variables due to dev/core#457

Fix incorrect sample filename

Update upgrade documentation to mention how to upgrade message templates

Add in documentation of as of 5.8 extensions can have examples loaded…

review.md - Split review standards into two buckets, "General" vs "Developer"

Add Civix example

Add "REF" (Refactor) as prefix for PR/git subjects

Under Hooks, switch the order of 'All Hooks' and 'Setup'

Currently we have 'All Hooks' followed by each of the categories of hooks
so it looks like 'Setup' is a hook category.  Its content is closer to 'Using Hooks'

Fix missing reference to pre/postJob hook files.

add more informatoin about creating an issue

CRM-21460 Add job execution hooks

Update setting metadata information

Remove reference to adding `CRM_Contact_BAO_Query::getGroupByFromSele…