Replaced Errors interface with concrete type Errors.

README.md

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