use response.js for all responses

results in:
1) less duplicated code
2) default response headers being used at all times
3) *all* requests being logged properly

- adds documentation for result.code
- allows using result.code to override HTTP 500
- uses response.js for too-busy, server error, method not allowed

lib/routes/avatars.js

@@ -23,13 +23,13 @@ function handle_default(img_status, userId, size, def, req, err, callback) {
       callback({
         status: img_status,
         redirect: newUrl,
-        err: err
+        err: err,
       });
     } else {
       callback({
         status: img_status,
         redirect: def,
-        err: err
+        err: err,
       });
     }
   } else {
@@ -44,7 +44,7 @@ function handle_default(img_status, userId, size, def, req, err, callback) {
         body: image,
         type: "image/png",
         hash: def,
-        err: resize_err || err
+        err: resize_err || err,
       });
     });
   }
@@ -62,7 +62,7 @@ module.exports = function(req, callback) {
     callback({
       status: -2,
       body: "Invalid Path",
-      code: 404
+      code: 404,
     });
     return;
   }
@@ -73,13 +73,13 @@ module.exports = function(req, callback) {
     // https://tools.ietf.org/html/rfc4918#page-78
     callback({
       status: -2,
-      body: "Invalid Size"
+      body: "Invalid Size",
     });
     return;
   } else if (!helpers.id_valid(userId)) {
     callback({
       status: -2,
-      body: "Invalid UserID"
+      body: "Invalid UserID",
     });
     return;
   }
@@ -101,7 +101,7 @@ module.exports = function(req, callback) {
           body: image,
           type: "image/png",
           err: err,
-          hash: hash
+          hash: hash,
         });
       } else {
         handle_default(status, userId, size, def, req, err, callback);