add config

config/source/source.go

@@ -0,0 +1,28 @@
+// Package source is the interface for sources
+package source
+
+import (
+	"time"
+)
+
+// Source is the source from which config is loaded
+type Source interface {
+	Read() (*ChangeSet, error)
+	Watch() (Watcher, error)
+	String() string
+}
+
+// ChangeSet represents a set of changes from a source
+type ChangeSet struct {
+	Data      []byte
+	Checksum  string
+	Format    string
+	Source    string
+	Timestamp time.Time
+}
+
+// Watcher watches a source for changes
+type Watcher interface {
+	Next() (*ChangeSet, error)
+	Stop() error
+}