cleaning before OTP conversion
	two files: client side/server side

new file:   pong_client.erl
renamed:    pong.erl -> pong_serv.erl
OTP refactoring

	pong_client now uses a gen_server behaviour

modified:   pong_client.erl
modified:   pong_serv.erl
pong server now is a finit state machine

modified:   pong_client.erl
modified:   pong_serv.erl