Adds a "staticRoutes" property on the server config

This lets a user define something like this:

```
    server:
      staticRoutes:
        '/javascripts': 'js'
        '/stylesheets': 'css'
        '/fonts': '<%= files.webfonts.root %>'
        '/images': '<%= files.img.root %>'
        '/bin': '/Users/justin/bin'
```

This is a ninja feature that I'm sneaking in to work on lineman-rails.
0.21.3