Fix guest embedding.

To prevent an Annotator is undefined error, the Constructor class is set
by the object returned from the hypothesisConfig function. The link to the
docs has also been updated. This unbreaks Epub.js.

h/static/scripts/annotator/main.js

@@ -47,22 +47,14 @@ require('./plugin/textquote');
 require('./plugin/textposition');
 require('./plugin/textrange');
 
-var Klass = Annotator.Host;
-var docs = 'https://github.com/hypothesis/h/blob/master/README.rst#customized-embedding';
+var docs = 'https://h.readthedocs.org/en/latest/hacking/customized-embedding.html';
 var options = {
   app: jQuery('link[type="application/annotator+html"]').attr('href'),
   BucketBar: {container: '.annotator-frame'},
-  Toolbar: {container: '.annotator-frame'}
+  Toolbar: {container: '.annotator-frame'},
+  Constructor: Annotator.Host
 };
 
-if (window.hasOwnProperty('hypothesisRole')) {
-  if (typeof window.hypothesisRole === 'function') {
-    Klass = window.hypothesisRole;
-  } else {
-    throw new TypeError('hypothesisRole must be a constructor function, see: ' + docs);
-  }
-}
-
 // Simple IE autodetect function
 // See for example https://stackoverflow.com/questions/19999388/jquery-check-if-user-is-using-ie/21712356#21712356
 var ua = window.navigator.userAgent;
@@ -81,5 +73,5 @@ if (window.hasOwnProperty('hypothesisConfig')) {
 }
 
 Annotator.noConflict().$.noConflict(true)(function () {
-  window.annotator = new Klass(document.body, options);
+  window.annotator = new options.Constructor(document.body, options);
 });