starting implementing an 'online' pong game application

new file:   src/pong.erl
	new: start_client
	new: client_loop
	new: start_server
	new: stop server
starting to implement graphic representation

modified:   pong.erl
	implemented: pong_str
	new: pong_str_aux
	new: line_str
end of the graphic representation

modified:   pong.erl
	implemented: line_str