Option: Additional directories/globs to watch

[mustardamus]

Currently only controller files (options.controllersPath/options.controllersGlob) are watched for changes. But maybe we need to remount the router when additional files are changing, these that are required in the controllers, eg. Models.

Lets have an option for additional files to watch:

watchFiles: [
  './models/*.js',
  './assets/**/*'
]

Additionally state in documentation to use https://github.com/sindresorhus/import-fresh in controllers.