Fix: #189 Respect base_url setting and serve content and assets

[ryanlelek]

Solves #189

To test:

• Clone repo
• make start
• Validate service on http://localhost:3000/
• Edit example/config.default.js to base_url: '/mydocs',
• Restart service
• Validate service on http://localhost:3000/mydocs/
• Stop service
• Validate multi-host of service by running node example/multiple-instances.js
• Validate service on http://localhost:3000/en/ and http://localhost:3000/es/
  ^ Note that the multiple-service script passes a nowrap setting to prevent a double-wrap, one from app/index.js and the other in the multiple-instances.js script itself, which would lead to http://localhost:3000/en/en/