add simple serverlet support:

* only one servlet name servlet1 could accessed using the URL (http://127.0.0.1/servlet1)
* servlet management is hard coded in the main method of Main class.
* when server is started:
** static resource placed int the directory webroot can accessed using URL http://127.0.0.1/filename
** if the server could not find neither the servlet nor the static file in the webroot directory,a "404"
   page will be reply to the visitor.