Disallow automatic creation of the routes and adds customized routes creation support

[giuseppeaiello]

This adds the following options:

• enablePathGeneration (default: true)
• routes (default: null)

Usage:

options: {
   //...
   enablePathGeneration: false,
   routes: require('./src/routes'),
   //...
}

Example of the ./src/routes.js file:

module.exports = [
    {
      path: '/projects', component: './src/pages/Index.vue', locale: 'en', slug: '/projects'
    },
    {
      path: '/progetti', component: './src/pages/Index.vue', locale: 'it', slug: '/projects'
    }
];