[feature request] support custom globals in pug templates

[greaterweb]

First off, great library! Just getting started using nucleus and it seems to loaded with potential.

For my test project I've copied the view templates locally to customize. All is working well but I'd really like attach some custom globals to the meta object which is available in the templates.

This could be implemented pretty easy but updating the render config. This might be something which makes sense to support only from the config file but I suppose it's possible to support as a CLI option as well. If time permits this week I'll try to submit a PR for the request to help you along.