Add domain and subdomain support for MinioAPI

This change brings in domain and subdomain support

   - ./minio --domain "yourminiodomain.com"

This change brings in a much needed feature by keeping
bucketnames as part of your 'DNS' name.

All your existing applications can be migrated off from s3 to
Minio without little to no modifications.

NOTE: Setting up DNS for your `buckets` is out of scope of this feature

pkg/api/minioapi/headers.go

@@ -27,6 +27,11 @@ import (
 	mstorage "github.com/minio-io/minio/pkg/storage"
 )
 
+// No encoder interface exists, so we create one.
+type encoder interface {
+	Encode(v interface{}) error
+}
+
 // Write Common Header helpers
 func writeCommonHeaders(w http.ResponseWriter, acceptsType string) {
 	w.Header().Set("Server", "Minio")