Add 'docs' well-known route for getting to a crate's documentation

Implements rust-lang#197.

Author: dirk

app/router.js

@@ -16,6 +16,9 @@ Router.map(function() {
     this.route('download');
     this.route('versions');
     this.route('reverse_dependencies');
+
+    // Well-known routes
+    this.route('docs');
   });
   this.route('me', function() {
     this.route('crates');

app/routes/crate/docs.js

@@ -0,0 +1,24 @@
+import Ember from 'ember';
+import Crate from 'cargo/models/crate';
+
+export default Ember.Route.extend({
+		afterModel: function(data) {
+        var crate;
+
+				if (data instanceof Crate) {
+						crate = data;
+				} else {
+						crate = data.crate;
+				}
+
+        var documentation = crate.get('documentation');
+
+        if (documentation) {
+            window.location = documentation;
+        } else {
+            // Redirect to the crate's main page if no documentation
+            // URL is found.
+            this.transitionTo('crate', crate);
+        }
+		}
+});