Issue #2502621 by Pravin Ajaaz, hussainweb, Peacog, jhodgdon, ivanjaros: Replace implement notes with inheritdoc tag

Issue #1392754 by tss, justAChris, jhodgdon: Comply with new documentation standards for @file for namespaced class files

Issue #2358079 by pwolanin, Berdir: Require a specific placeholder format in db_query() in order to trigger argument expansion, and require explicit 'IN' parameter for conditions

Issue #2057809 by StephaneQ, Berdir, chx, dawehner: Fix up param/return documentation in database API

Initial move and rename of database classes to PSR-0 namespaces.  So far only MySQL has been converted.