Alchem._urlCheck not recognizing certain URLs

So, Alchemy._urlCheck was failing for URLs with special characters in the, such as "~". Some RSS feeds I was working with were giving me major problems with this, so I adjusted the urlCheck logic to use Node's `url` module to detect if a hostname and protocol could be found. I also throw out any URL that contains spaces, which helps with test cases like the one included on line 23 of `test/index.js`.