implement xkcd functionality

The strings.json file is extensible; other fields that can be
placed in the xkcd string include the {year}, {month} and {day}
of the comic; the {alt} text; and links to the {img}.
A {transcript} is also available.

modules/link/link.js

@@ -32,6 +32,24 @@ var link = function(dbot) {
             }
             this.fetchTitle(event, link);
         },
+        
+        '~xkcd': function(event) {
+            var comicId = event.params[1];
+            if(comicId){
+                comicId = comicId + "/";
+            } else {
+                comicId = "";
+            }
+            var link = "http://xkcd.com/"+comicId+"info.0.json";
+            request(link,  function(error, response, body) {
+                if (response.statusCode == "200") {
+                    data = JSON.parse(body);
+                    event.reply(dbot.t("xkcd",data));
+                } else {
+                    event.reply(dbot.t("no-hits"));
+                }
+            });
+        },
 
         '~ud': function(event) {
 	    var query = event.input[1];

modules/link/strings.json

@@ -2,5 +2,11 @@
     "title_not_found": {
         "english": "No page title found.",
         "na'vi": "Oel ke tsun run 'upxare atxin."
+    },
+    "xkcd": {
+        "english": "xkcd {num}: {title} https://xkcd.com/{num}"
+    },
+    "no-hits": {
+        "english": "No hits."
     }
 }