ARI: Improve wiki documentation

This patch improves the documentation of ARI on the wiki. Specifically, it
addresses the following:
* Allowed values and allowed ranges weren't documented. This was particularly
  frustrating, as Asterisk would reject query parameters with disallowed values
  - but we didn't tell anyone what the allowed values were.
* The /play/id operation on /channels and /bridges failed to document all of
  the added media resource types.
* Documentation for creating a channel into a Stasis application failed to
  note when it occurred, and that creating a channel into Stasis conflicts with
  creating a channel into the dialplan.
* Some other minor tweaks in the mustache templates, including italicizing the
  parameter type, putting the default value on its own sub-bullet, and some
  other nicities.

Review: https://reviewboard.asterisk.org/r/4351
........

Merged revisions 431145 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@431148 65c4cc65-6c06-0410-ace0-fbb531ad65f3

rest-api-templates/asterisk_processor.py

@@ -223,6 +223,10 @@ class AsteriskProcessor(SwaggerPostProcessor):
         else:
             parameter.c_space = ' '
         parameter.wiki_description = wikify(parameter.description)
+        if parameter.allowable_values:
+            parameter.wiki_allowable_values = parameter.allowable_values.to_wiki()
+        else:
+            parameter.wiki_allowable_values = None
 
     def process_model(self, model, context):
         model.description_dox = model.description.replace('\n', '\n * ')