Hide passwords when user is prompted

This change makes it so that the server sends an "I will echo" command to the telnet client when the user gets prompted for his or her password. This effectively hides the password, because the user's client will stop echoing. Afterwards, an "I won't echo" command is sent to inform the client to resume its own echoing.

This PR also includes minor changes to .gitignore.

Additionally, the server tries to create the "./players" directory on startup, which needs to exist otherwise no player data can be successfully saved.