Remove the word middleware (#1067)

* Rename middleware to plugin

first pass; mostly used 'sed', few spots where I manually changed
text.

This still builds a coredns binary.

* fmt error

* Rename AddMiddleware to AddPlugin

* Readd AddMiddleware to remain backwards compat

plugin/etcd/README.md

@@ -0,0 +1,109 @@
+# etcd
+
+*etcd* enables reading zone data from an etcd instance. The data in etcd has to be encoded as
+a [message](https://github.com/skynetservices/skydns/blob/2fcff74cdc9f9a7dd64189a447ef27ac354b725f/msg/service.go#L26)
+like [SkyDNS](https://github.com/skynetservices/skydns). It should also work just like SkyDNS.
+
+The etcd plugin makes extensive use of the proxy plugin to forward and query other servers
+in the network.
+
+## Syntax
+
+~~~
+etcd [ZONES...]
+~~~
+
+* **ZONES** zones etcd should be authoritative for.
+
+The path will default to `/skydns` the local etcd proxy (http://localhost:2379).
+If no zones are specified the block's zone will be used as the zone.
+
+If you want to `round robin` A and AAAA responses look at the `loadbalance` plugin.
+
+~~~
+etcd [ZONES...] {
+    stubzones
+    fallthrough
+    path PATH
+    endpoint ENDPOINT...
+    upstream ADDRESS...
+    tls CERT KEY CACERT
+}
+~~~
+
+* `stubzones` enables the stub zones feature. The stubzone is *only* done in the etcd tree located
+    under the *first* zone specified.
+* `fallthrough` If zone matches but no record can be generated, pass request to the next plugin.
+* **PATH** the path inside etcd. Defaults to "/skydns".
+* **ENDPOINT** the etcd endpoints. Defaults to "http://localhost:2397".
+* `upstream` upstream resolvers to be used resolve external names found in etcd (think CNAMEs)
+  pointing to external names. If you want CoreDNS to act as a proxy for clients, you'll need to add
+  the proxy plugin. **ADDRESS** can be an IP address, and IP:port or a string pointing to a file
+  that is structured as /etc/resolv.conf.
+* `tls` followed by:
+  * no arguments, if the server certificate is signed by a system-installed CA and no client cert is needed
+  * a single argument that is the CA PEM file, if the server cert is not signed by a system CA and no client cert is needed
+  * two arguments - path to cert PEM file, the path to private key PEM file - if the server certificate is signed by a system-installed CA and a client certificate is needed
+  * three arguments - path to cert PEM file, path to client private key PEM file, path to CA PEM file - if the server certificate is not signed by a system-installed CA and client certificate is needed
+
+## Examples
+
+This is the default SkyDNS setup, with everying specified in full:
+
+~~~
+.:53 {
+    etcd skydns.local {
+        stubzones
+        path /skydns
+        endpoint http://localhost:2379
+        upstream 8.8.8.8:53 8.8.4.4:53
+    }
+    prometheus
+    cache 160 skydns.local
+    loadbalance
+    proxy . 8.8.8.8:53 8.8.4.4:53
+}
+~~~
+
+Or a setup where we use `/etc/resolv.conf` as the basis for the proxy and the upstream
+when resolving external pointing CNAMEs.
+
+~~~
+.:53 {
+    etcd skydns.local {
+        path /skydns
+        upstream /etc/resolv.conf
+    }
+    cache 160 skydns.local
+    proxy . /etc/resolv.conf
+}
+~~~
+
+
+### Reverse zones
+
+Reverse zones are supported. You need to make CoreDNS aware of the fact that you are also
+authoritative for the reverse. For instance if you want to add the reverse for 10.0.0.0/24, you'll
+need to add the zone `0.0.10.in-addr.arpa` to the list of zones. (The fun starts with IPv6 reverse zones
+in the ip6.arpa domain.) Showing a snippet of a Corefile:
+
+~~~
+    etcd skydns.local 0.0.10.in-addr.arpa {
+        stubzones
+    ...
+~~~
+
+Next you'll need to populate the zone with reverse records, here we add a reverse for
+10.0.0.127 pointing to reverse.skydns.local.
+
+~~~
+% curl -XPUT http://127.0.0.1:4001/v2/keys/skydns/arpa/in-addr/10/0/0/127 \
+    -d value='{"host":"reverse.skydns.local."}'
+~~~
+
+Querying with dig:
+
+~~~
+% dig @localhost -x 10.0.0.127 +short
+reverse.atoom.net.
+~~~