Implemented a Bzip2Encoder

Motivation:

Bzip2Encoder provides sending data compressed in bzip2 format.

Modifications:

Added classes:
- Bzip2Encoder
- Bzip2BitWriter
- Bzip2BlockCompressor
- Bzip2DivSufSort
- Bzip2HuffmanAllocator
- Bzip2HuffmanStageEncoder
- Bzip2MTFAndRLE2StageEncoder
- Bzip2EncoderTest

Modified classes:
- Bzip2Constants (splited BLOCK_HEADER_MAGIC and END_OF_STREAM_MAGIC)
- Bzip2Decoder (use splited magic numbers)

Added integration tests for Bzip2Encoder/Decoder

Result:

Implemented new encoder which can compress outgoing data in bzip2 format.

NOTICE.txt

@@ -89,6 +89,15 @@ and decompression library written by Matthew J. Francis. It can be obtained at:
   * HOMEPAGE:
     * https://code.google.com/p/jbzip2/
 
+This product contains a modified portion of 'libdivsufsort', a C API library to construct
+the suffix array and the Burrows-Wheeler transformed string for any input string of
+a constant-size alphabet written by Yuta Mori. It can be obtained at:
+
+  * LICENSE:
+    * license/LICENSE.libdivsufsort.txt (MIT License)
+  * HOMEPAGE:
+    * https://code.google.com/p/libdivsufsort/
+
 This product optionally depends on 'JZlib', a re-implementation of zlib in
 pure Java, which can be obtained at:
 

codec/src/main/java/io/netty/handler/codec/compression/Bzip2BitWriter.java

@@ -0,0 +1,109 @@
+/*
+ * Copyright 2014 The Netty Project
+ *
+ * The Netty Project licenses this file to you under the Apache License,
+ * version 2.0 (the "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at:
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+package io.netty.handler.codec.compression;
+
+import io.netty.buffer.ByteBuf;
+
+/**
+ * A bit writer that allows the writing of single bit booleans, unary numbers, bit strings
+ * of arbitrary length (up to 24 bits), and bit aligned 32-bit integers. A single byte at a
+ * time is written to the {@link ByteBuf} when sufficient bits have been accumulated.
+ */
+final class Bzip2BitWriter {
+    /**
+     * A buffer of bits waiting to be written to the output stream.
+     */
+    private int bitBuffer;
+
+    /**
+     * The number of bits currently buffered in {@link #bitBuffer}.
+     */
+    private int bitCount;
+
+    /**
+     * Writes up to 24 bits to the output {@link ByteBuf}.
+     * @param count The number of bits to write (maximum {@code 24}, because the {@link #bitBuffer}
+     *              is {@code int} and it can store up to {@code 8} bits before calling)
+     * @param value The bits to write
+     */
+    void writeBits(ByteBuf out, final int count, final int value) {
+        if (count < 0 || count > 24) {
+            throw new IllegalArgumentException("count: " + count + " (expected: 0-24)");
+        }
+        int bitCount = this.bitCount;
+        int bitBuffer = this.bitBuffer | (value << (32 - count)) >>> bitCount;
+        bitCount += count;
+
+        while (bitCount >= 8) {
+            out.writeByte(bitBuffer >>> 24);
+            bitBuffer <<= 8;
+            bitCount -= 8;
+        }
+        this.bitBuffer = bitBuffer;
+        this.bitCount = bitCount;
+    }
+
+    /**
+     * Writes a single bit to the output {@link ByteBuf}.
+     * @param value The bit to write
+     */
+    void writeBoolean(ByteBuf out, final boolean value) {
+        int bitCount = this.bitCount + 1;
+        int bitBuffer = this.bitBuffer | (value ? 1 : 0) << (32 - bitCount);
+
+        if (bitCount == 8) {
+            out.writeByte(bitBuffer >>> 24);
+            bitBuffer = 0;
+            bitCount = 0;
+        }
+        this.bitBuffer = bitBuffer;
+        this.bitCount = bitCount;
+    }
+
+    /**
+     * Writes a zero-terminated unary number to the output {@link ByteBuf}.
+     * Example of the output for value = 6: {@code 1111110}
+     * @param value The number of {@code 1} to write
+     */
+    void writeUnary(ByteBuf out, int value) {
+        if (value < 0) {
+            throw new IllegalArgumentException("value: " + value + " (expected 0 or more)");
+        }
+        while (value-- > 0) {
+            writeBoolean(out, true);
+        }
+        writeBoolean(out, false);
+    }
+
+    /**
+     * Writes an integer as 32 bits to the output {@link ByteBuf}.
+     * @param value The integer to write
+     */
+    void writeInt(ByteBuf out, final int value) {
+        writeBits(out, 16, (value >>> 16) & 0xffff);
+        writeBits(out, 16, value & 0xffff);
+    }
+
+    /**
+     * Writes any remaining bits to the output {@link ByteBuf},
+     * zero padding to a whole byte as required.
+     */
+    void flush(ByteBuf out) {
+        if (bitCount > 0) {
+            writeBits(out, 8 - bitCount, 0);
+        }
+    }
+}