Protection for sv_password and rcon_password cvars

[nekonomicon]

I think need to add some things to protect passwords on server side:

• fast and hard hashing algorithm(like MurMurHash) with salt.
• timing attack protection(timingsafe_memcmp from OpenBSD/LibreSSL).
• additional pause in seconds between authentifications(2 seconds or more, may be tune value via cvar).
• fail2ban analog.