add a standard interface that wraps ReadByte, io.ReadByter

R=rsc
CC=golang-dev
https://golang.org/cl/181163

src/pkg/io/io.go

@@ -150,6 +150,14 @@ type WriterAt interface {
 	WriteAt(p []byte, off int64) (n int, err os.Error)
 }
 
+// ReadByter is the interface that wraps the ReadByte method.
+//
+// ReadByte reads and returns the next byte from the input.
+// If no byte is available, err will be set.
+type ReadByter interface {
+	ReadByte() (c byte, err os.Error)
+}
+
 // WriteString writes the contents of the string s to w, which accepts an array of bytes.
 func WriteString(w Writer, s string) (n int, err os.Error) {
 	return w.Write(strings.Bytes(s))