accept server instance as an option, so it may intergrate with other app...

with this pr, you can use it with express like : 


```
var express = require('express'),
  app = express(),
  http = require("http"),
  server = http.createServer(app)

flo(PATH_TO_DIR,{
    server:server,
    glob:[
      '**/*.css',
      '**/*.html',
      '**/*.jade'
    ]},function( filepath, callback){

      callback({
        resourceURL : resourceURL,
        contents : fs.readFileSync(path.join(root,filepath)),
        update : function( _window,_resourceURL){
        }
      })
    }
  })
```