Default theme handlebars version added
Template engine agnostic

Jade is the default template engine from now on, but can be changed
within the velcro.json configuration file key `template_engine` to set
it, for example, as `hbs` to use handlebars template engine.

It will require, dough, to install `node_modules/hbs` which  can
quickly be done using the no-vanilla version and adding the dependency
to the package.json file.