Separate file system doc

http://www.writethedocs.org/guide/writing/docs-principles/#cumulative
Creating a new entity should come before creating a database upgrader

spelling error

Nice documentation :) I didn't realise it existed :)

MySQL query log

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.