Support for `hostname_alter` directive in the listener section of sniproxy.conf.
This directive is applied only if the target is `*` i.e. use the hostname that the client requested.
If applied, this directive deletes a substring in the hostname. The substring is the first argument to this directive.
For example:
listener 0.0.0.0:443 {
    protocol tls
    table backend

    # Alter external-foo.bar.com foo.bar.com
    hostname_alter backup-
}
Merge branch 'master' of https://github.com/aniapte/sniproxy