Implement chaos middleware

This allows for CH TXT queries that return some information about
the server and/or the authors (or whatever you put in there).

middleware/chaos/chaos.md

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+# chaos
+
+`chaos`
+
+## Syntax
+
+~~~
+chaos [version] [authors...]
+~~~
+
+* `version` the version to return, defaults to CoreDNS.
+* `authors` what authors to return. No default.
+
+## Examples
+
+~~~
+etcd {
+    path /skydns
+    endpoint endpoint...
+    stubzones
+}
+~~~
+
+* `path` /skydns
+* `endpoint` endpoints...
+* `stubzones`