Allow tags to be send by URL instead of HTTP header

This is a pull request for a temporary fix for this issue
https://github.com/nodejitsu/node-loggly/issues/35

It allows the selection of sending tags as part of the URI instead of the HTTP header X-LOGGLY-TAG. To use the URI option, do:
``` js
    var loggly = require('loggly');
  
    var client = loggly.createClient({
      token: "your-really-long-input-token",
      subdomain: "your-subdomain",
      auth: {
        username: "your-username",
        password: "your-password"
      },
      useTagHeader: false
    });
```

If the option is not set, the client will behave as it would normally.