unbound helper supports bound helper static strings
[DOC beta] Generate documentation for ember-extension-support.

Cleans up the docs, and adds the package to the `YUIDoc` config.
Merge pull request #3977 from sly7-7/unbound-with-bound-and-statics

[BUGFIX Beta] unbound helper supports bound helper static strings
Merge pull request #4024 from rjackson/document_ember_extension_support

[DOC beta] Generate documentation for ember-extension-support.