update common config interface

internal/cnf/common.go

@@ -1,5 +1,9 @@
 package cnf
 
+import (
+	"io"
+)
+
 // Field generic representation (root, branch or leaf)
 type Field struct {
 	// Label of the current field
@@ -12,6 +16,9 @@ type Field struct {
 
 // ConfigurationFormat is the common interface for all configuration parser
 type ConfigurationFormat interface {
+	// Parse the given file
+	Parse(io.Reader) error
+
 	// Get the value of a field if it exists
 	Get(string) (string, bool)