Doc: add package docs (#296)

* Doc: add package docs

Add short package level docs to make godoc looks nicer.
Add some badges to the README.

* correct url

README.md

 # CoreDNS
 
+ [![Documentation](https://img.shields.io/badge/godoc-reference-blue.svg?style=flat-square)](https://godoc.org/github.com/miekg/coredns)
+ [![Build Status](https://img.shields.io/travis/miekg/coredns.svg?style=flat-square&label=build)](https://travis-ci.org/miekg/coredns)
+
 CoreDNS is a DNS server that started as a fork of [Caddy](https://github.com/mholt/caddy/). It has the
 same model: it chains middleware. In fact it's so similar that CoreDNS is now a server type plugin for
 Caddy.

core/coredns.go

+// Package core registers the server and all plugins we support.
 package core
 
 import (

core/dnsserver/server.go

+// Package DNS server implements all the interfaces from Caddy, so that
+// CoreDNS can be a servertype plugin.
 package dnsserver
 
 import (

coremain/run.go

+// Package coremain contains the functions for starting CoreDNS.
 package coremain
 
 import (

middleware/bind/bind.go

+// Package bind allows binding to a specific interface instead of bind to all of them.
 package bind
 
 import "github.com/mholt/caddy"

middleware/chaos/chaos.go

+// Package chaos implements a middleware that answer to 'CH version.bind TXT' type queries.
 package chaos
 
 import (

middleware/dnssec/dnssec.go

+// Package dnssec implements a middleware that signs responses on-the-fly using
+// NSEC black lies.
 package dnssec
 
 import (

middleware/etcd/etcd.go

-// Package etcd provides the etcd backend.
+// Package etcd provides the etcd backend middleware.
 package etcd
 
 import (

middleware/etcd/msg/service.go

+// Package msg defines the Service structure which is used for service discovery.
 package msg
 
 import (

middleware/file/file.go

+// Package file implements a file backend.
 package file
 
 import (

middleware/health/health.go

+// Package health implements an HTTP handler that responds to health checks.
 package health
 
 import (

middleware/kubernetes/kubernetes.go

@@ -17,8 +17,8 @@ import (
 	"github.com/miekg/dns"
 	"k8s.io/kubernetes/pkg/api"
 	unversionedapi "k8s.io/kubernetes/pkg/api/unversioned"
-	unversionedclient "k8s.io/kubernetes/pkg/client/unversioned"
 	"k8s.io/kubernetes/pkg/client/restclient"
+	unversionedclient "k8s.io/kubernetes/pkg/client/unversioned"
 	"k8s.io/kubernetes/pkg/client/unversioned/clientcmd"
 	clientcmdapi "k8s.io/kubernetes/pkg/client/unversioned/clientcmd/api"
 	"k8s.io/kubernetes/pkg/labels"

middleware/loadbalance/loadbalance.go

+// Package loadbalance shuffles A and AAAA records.
 package loadbalance
 
 import (

middleware/metrics/metrics.go

+// Package metrics implement a handler and middleware that provides Prometheus
+// metrics.
 package metrics
 
 import (

middleware/pkg/dnsrecorder/recorder.go

+// Package dnsrecorder allows you to record a DNS response when it is send to the client.
 package dnsrecorder
 
 import (

middleware/pkg/dnsutil/doc.go

+// Package dnsutil contains DNS related helper functions.
+package dnsutil

middleware/pkg/edns/edns.go

+// Package edns provides function usefull for adding/inspecting OPT records to/in messages.
 package edns
 
 import (

middleware/pkg/storage/fs.go

+// Package storage abstracts away where middleware can store assests (zones, keys, etc).
 package storage
 
 import (

middleware/pprof/pprof.go

+// Package pprof implement a debug endpoint for getting profiles using the
+// go pprof tooling.
 package pprof
 
 import (

middleware/secondary/secondary.go

+// Package secondary implements a secondary middleware.
 package secondary
 
 import "github.com/miekg/coredns/middleware/file"

middleware/test/doc.go

+// Package test contains helper functions for writing middleware tests.
+package test

middleware/whoami/whoami.go

+// Package whoami implements a middleware that returns details about the resolving
+// querying it.
 package whoami
 
 import (

request/request.go

+// Package requests abstract a client's request so that all middleware
+// will handle them in an unified way.
 package request
 
 import (

test/doc.go

+// Package test contains function and types useful for writing tests
+package test