This version will use the standalone (netcat) mode of acme.sh during
verification instead of exposing uhttpd to the internet for the duration
of the verification. It will also add an ip6tables rule to also support
verification over IPv6.

Also contains an updated version of acme.sh.

Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>

This adds a Luci configuration app for the ACME certificate package.

Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>

This adds a package wrapping the acme.sh script from
https://github.com/Neilpang/acme.sh in Uci config and hooks to interact
correctly with uhttpd.

Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>