feat(model): adds model name inference from url.

Also improves $name method to be able to return the plural name version.
feat(packer_cache): changed to expect plural resource names
feat(builder): makes packer a configuration option settable as __packer__

Also injects packer in factory and not in builder.
feat(builder): changes the __var__ format for model config to all caps VAR format
feat(): adds the default packer!

Closes #62