res_pjsip_history: Add a module that provides PJSIP history for debugging

This patch adds a new module, res_pjsip_history, that provides a slightly
better way of debugging SIP message traffic on a busy Asterisk system. The
existing mechanisms all rely on passively dumping a SIP message to the CLI.
While this is perfectly fine for logging purposes and well controlled
environments, on many installations, the amount of SIP messages Asterisk
receives will quickly swamp the CLI. This makes it difficult to view/capture
those messages that you want to diagnose in real time.

This patch provides another way of handling this. When enabled, the module
will store SIP message traffic in memory. This traffic can then be queried
at leisure.

In order to make the querying useful, a CLI command has been implemented,
'pjsip show history', that supports a basic expression syntax similar to
SQL or other query languages. A small number of useful fields have been
added in this initial patch; additional fields can easily be added in
later improvements. Those fields are:
 - number: The entry index in the history
 - timestamp: The time the message was recieved
 - addr: The source/destination address of the message
 - sip.msg.request.method: The request method
 - sip.msg.call-id: The Call-ID header

Note - this is a resurrection of the module initially proposed on Review Board
here: https://reviewboard.asterisk.org/r/4053/

Change-Id: I39bd74ce998e99ad5ebc0aab3e84df3a150f8e36

CHANGES

@@ -201,6 +201,31 @@ Queue
  * Added field ReasonPause on QueueMemberStatus if set when paused, the reason
    the queue member was paused.
 
+------------------------------------------------------------------------------
+--- Functionality changes from Asterisk 13.7.0 to Asterisk 13.8.0 ------------
+------------------------------------------------------------------------------
+
+res_pjsip_history
+------------------
+ * A new module, res_pjsip_history, has been added that provides SIP history
+   viewing/filtering from the CLI. The module is intended to be used on systems
+   with busy SIP traffic, where existing forms of viewing SIP messages - such
+   as the res_pjsip_logger - may be inadequate. The module provides two new
+   CLI commands:
+   - 'pjsip set history {on|off|clear}' - this enables/disables SIP history
+     capturing, as well as clears an existing history capture. Note that SIP
+     packets captured are stored in memory until cleared. As a result, the
+     history capture should only be used for debugging/viewing purposes, and
+     should *NOT* be left permanently enabled on a system.
+   - 'pjsip show history' - displays the captured SIP history. When invoked
+     with no options, the entire captured history is displayed. Two options
+     are available:
+     -- 'entry <num>' - display a detailed view of a single SIP message in
+        the history
+     -- 'where ...' - filter the history based on some expression. For more
+        information on filtering, view the current CLI help for the
+        'pjsip show history' command.
+
 ------------------------------------------------------------------------------
 --- Functionality changes from Asterisk 13.6.0 to Asterisk 13.7.0 ------------
 ------------------------------------------------------------------------------