Reimplement nodoc handling to be less buggy and more useful (#1471)

* Remove old nodoc support and rename isPublic/isPrivate to something more indicative of the limited features of each

* Getting there, but still need to work out fields/TopLevelVariables

* Integration tests

* Add unit tests for nodoc

* A few more tests

* dartfmt

Author: jcollins-g

lib/dartdoc.dart

@@ -487,7 +487,7 @@ class DartDoc {
       sources.add(source);
       if (context.computeKindOf(source) == SourceKind.LIBRARY) {
         LibraryElement library = context.computeLibraryElement(source);
-        if (!isPrivate(library)) libraries.add(library);
+        if (!hasPrivateName(library)) libraries.add(library);
       }
     }