Locking: Add locked attribute to api

Add boolean `locked` attribute to api json response. Add `/api/lock`
and `/api/unlock` to api documentation.

r2/r2/controllers/api.py

@@ -1407,8 +1407,11 @@ class ApiController(RedditController):
                 VModhash(),
                 VSrCanBan('id'),
                 thing=VByName('id', thing_cls=Link))
+    @api_doc(api_section.links_and_comments)
     def POST_lock(self, thing):
-        """Lock a comment thread.
+        """Lock a link.
+
+        Prevents a post from receiving new comments.
 
         See also: [/api/unlock](#POST_api_unlock).
 
@@ -1426,14 +1429,16 @@ class ApiController(RedditController):
         ModAction.create(thing.subreddit_slow, c.user, target=thing,
                          action='lock')
 
-
     @require_oauth2_scope("modposts")
     @noresponse(VUser(),
                 VModhash(),
                 VSrCanBan('id'),
                 thing=VByName('id', thing_cls=Link))
+    @api_doc(api_section.links_and_comments)
     def POST_unlock(self, thing):
-        """Unlock a comment thread.
+        """Unlock a link.
+
+        Allow a post to receive new comments.
 
         See also: [/api/lock](#POST_api_lock).
 

r2/r2/lib/jsontemplates.py

@@ -621,6 +621,7 @@ class LinkJsonTemplate(ThingJsonTemplate):
         likes="likes",
         link_flair_css_class="flair_css_class",
         link_flair_text="flair_text",
+        locked="locked",
         media="media_object",
         media_embed="media_embed",
         num_comments="num_comments",