Replaced Errors interface with concrete type Errors.

README.md

@@ -35,11 +35,12 @@ function Open(p string) (*File, error) {
 
 **Errors**
 
-An `Errors` struct that represents multiple errors (but still adheres to the `error` interface)
+An `Errors` interface that represents multiple errors (but still adheres to the `error` interface)
 
 ```
-type Errors struct {
-	Errs []error
+type Errors interface {
+    error
+    Errs() []error
 }
 ```