Update config framework/sorcery with types/options without documentation

There are times when a configuration option should not have documentation.

1. Some options are registered with a particular object merely as a warning to
   users. These options aren't even really 'deprecated' - which has its own
   separate API call - they are actually provided by a different configuration
   file. The options are merely registered so that the user gets a warning that
   a different configuration file provides the item.

2. Some object types - most notably some used by modules that use sorcery - are
   completely internal and should never be shown to the user.

3. Sorcery itself has several 'hidden' fields that should never be shown to a
   user.

This patch updates the configuration framework and sorcery with additional API
calls that allow a module to register types as internal and options as not
requiring documentation. This bypasses the XML documentation checking.

This patch also re-enables the strict XML documentation checking in trunk, as
well as updates some documentation that was missing.

Review: https://reviewboard.asterisk.org/r/2785/

(closes issue ASTERISK-22359)
Reported by: Matt Jordan

(closes issue ASTERISK-22112)
Reported by: Rusty Newton



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@397524 65c4cc65-6c06-0410-ace0-fbb531ad65f3