Release 0.1.1

• If someone try to initialize url-extract module more than one time, it will throw a error. For example:

var urlExtract = require('url-extract')(); // initialize first time
var urlExtract = require('url-extract')({
  workerNum: 50
}); // initizlize second time, throw a error

// Because some options like 'workerNum' could not change after initialization, 
// we prevent user do this and unknown error occurred.

var urlExtract = require('url-extract')(); 
// This does not throw an error, it's just get the url-extract module