Add an example for Writer.Reset.

It is based on the one for flate.Writer.Reset.

Fixes #31.

example_test.go

@@ -0,0 +1,53 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package brotli
+
+import (
+	"bytes"
+	"io"
+	"log"
+	"os"
+)
+
+func ExampleWriter_Reset() {
+	proverbs := []string{
+		"Don't communicate by sharing memory, share memory by communicating.\n",
+		"Concurrency is not parallelism.\n",
+		"The bigger the interface, the weaker the abstraction.\n",
+		"Documentation is for users.\n",
+	}
+
+	var b bytes.Buffer
+
+	bw := NewWriter(nil)
+	br := NewReader(nil)
+
+	for _, s := range proverbs {
+		b.Reset()
+
+		// Reset the compressor and encode from some input stream.
+		bw.Reset(&b)
+		if _, err := io.WriteString(bw, s); err != nil {
+			log.Fatal(err)
+		}
+		if err := bw.Close(); err != nil {
+			log.Fatal(err)
+		}
+
+		// Reset the decompressor and decode to some output stream.
+		if err := br.Reset(&b); err != nil {
+			log.Fatal(err)
+		}
+		if _, err := io.Copy(os.Stdout, br); err != nil {
+			log.Fatal(err)
+		}
+	}
+
+	// Output:
+	// Don't communicate by sharing memory, share memory by communicating.
+	// Concurrency is not parallelism.
+	// The bigger the interface, the weaker the abstraction.
+	// Documentation is for users.
+}