[documentation/feature] Consul/etcd support atomic multiple key changes now

[strarsis]

According to current traefik documentation, Consul and etcd backends
do not support updating multiple keys atomically.

However, the referenced issues for consul and etcd have been closed.
Wouldn't this also mean that this feature can be deprecated now
(maybe still useful for older consul and etcd servers)?

[emilevauge]

@strarsis We use https://github.com/docker/libkv to abstract kv stores connections. Until this feature is supported in libkv, we still need to use the hacky way http://docs.traefik.io/v1.0/toml/#atomic-configuration-changes.

[strarsis]

So an issue is left in libkv and not in Consul or etcd.

[Leon99]

It's been a while and it looks like libkv supports it now:

It's possible that I'm looking at a wrong thing though, @emilevauge if this is the case, could you possibly link libkv issue re. Consul support so we could track that?