feature request: backup/restore

[amkuipers]

Request to add a feature to be able to backup and restore the hosts file using hed.

Examples:

$ hed backup
backup /etc/hosts made to ~/hosts.bak
$ hed restore
restored /etc/hosts from ~/hosts.bak

$ hed backup /tmp/x
backup /etc/hosts made to /tmp/x
$ hed restore /tmp/x
restored /etc/hosts from /tmp/x

[credmp]

Really good feature, wondering if it can work together with #25.