Add docs.rs integration

When a crate does not specify a documentation link, we query docs.rs to know
if the documentation for the requested version was successfully built. If
if is, we set the crate's documentation link to the corresponding docs.rs
page, if not nothing changes.

Author: kureuil

app/routes/crate/version.js

@@ -68,6 +68,17 @@ export default Ember.Route.extend({
                 .finally(() => controller.set('fetchingFollowing', false));
         }
 
+        if (!crate.get('documentation')) {
+            let crateName = crate.get('name');
+            let crateVersion = params.version_num;
+            ajax(`https://docs.rs/crate/${crateName}/${crateVersion}/builds.json`)
+                .then((r) => {
+                    if (r.length > 0 && r[0].build_status === true) {
+                        crate.set('documentation', `https://docs.rs/${crateName}/${crateVersion}/${crateName}/`);
+                    }
+                });
+        }
+
         // Find version model
         return crate.get('versions')
             .then(versions => {