Auto-save and multi-distro support

[khor0]

Hey,

My major issues are resolved here, which contain:

• Using /sbin/iptables may not work for everybody. This is resolved by loading the path from the which command
• No auto-save. Had to look around until I've realized it was in the README. Now it prompts the user if he wants to save the configuration
• IPv6 was not handled. The least I can do is change all policies to DROP to not give false sense of security by using this script
• Printing rules are redundant. People should know what they're running on their machines. So, I prompt the user to print the new rules.

I've only added auto-save support to Arch and CentOS.

[Exosunandnet]

thanks for the contribution