User Guide - DB Driver Reference

First stab at DB driver reference. Methods are listed in order encountered in the source file.
Parameter or return types in DB_driver updated as needed, and reflected here.
TOC entry added to bottom of database index page.
Signed-off-by:James L Parry <jim_parry@bcit.ca>
Merge pull request #3416 from jim-parry/userguide/db_driver_reference

User Guide - DB Driver Reference