Update links for actual Protobuf repo and documentation

Motivation:

Use actual links to new locations of Protobuf repo and documentation to
avoid problems when redirect will not work.

Modification:

Links in comments and all/pom.xml

Result:

Correct links to Protobuf resources

all/pom.xml

@@ -72,7 +72,7 @@
                     <groupId>com.puppycrawl.tools</groupId>
                     <artifactId>checkstyle</artifactId>
                   </exclusion>
-                </exclusions> 
+                </exclusions>
               </dependency>
               <dependency>
                 <groupId>com.puppycrawl.tools</groupId>
@@ -104,7 +104,7 @@
               <detectJavaApiLink>false</detectJavaApiLink>
               <additionalparam>
                 -link http://docs.oracle.com/javase/7/docs/api/
-                -link http://code.google.com/apis/protocolbuffers/docs/reference/java/
+                -link https://developers.google.com/protocol-buffers/docs/reference/java/
                 -link http://docs.oracle.com/javaee/6/api/
                 -link http://www.slf4j.org/apidocs/
                 -link https://commons.apache.org/proper/commons-logging/apidocs/

codec/src/main/java/io/netty/handler/codec/protobuf/ProtobufVarint32FrameDecoder.java

@@ -27,7 +27,7 @@ import com.google.protobuf.CodedInputStream;
 /**
  * A decoder that splits the received {@link ByteBuf}s dynamically by the
  * value of the Google Protocol Buffers
- * <a href="http://code.google.com/apis/protocolbuffers/docs/encoding.html#varints">Base
+ * <a href="https://developers.google.com/protocol-buffers/docs/encoding#varints">Base
  * 128 Varints</a> integer length field in the message.  For example:
  * <pre>
  * BEFORE DECODE (302 bytes)       AFTER DECODE (300 bytes)

codec/src/main/java/io/netty/handler/codec/protobuf/package-info.java

@@ -16,7 +16,7 @@
 
 /**
  * Encoder and decoder which transform a
- * <a href="http://code.google.com/p/protobuf/">Google Protocol Buffers</a>
+ * <a href="https://github.com/google/protobuf">Google Protocol Buffers</a>
  * {@link com.google.protobuf.Message} into a {@link io.netty.buffer.ByteBuf}
  * and vice versa.
  */