Remove Watch() from Provider interface

Closes knadh#45

interfaces.go

@@ -11,11 +11,6 @@ type Provider interface {
 	// It is important to note that the string keys should not be flat delimited
 	// keys like `parent.child.key`, but nested like `{parent: {child: {key: 1}}}`.
 	Read() (map[string]interface{}, error)
-
-	// Watch watches the source for changes, for instance, changes to a file,
-	// and invokes a callback with an `event` interface, which a provider
-	// is free to substitute with its own type, including nil.
-	Watch(func(event interface{}, err error)) error
 }
 
 // Parser represents a configuration format parser.