Remove unnecessary finally block
Give a handler more control over how its buffers' read bytes are discarded.

This pull request adds two new handler methods: discardInboundReadBytes(ctx) and discardOutboundReadBytes(ctx) to ChannelInboundByteHandler and ChannelOutboundByteHandler respectively. They are called between every inboundBufferUpdated() and flush() respectively. Their default implementation is to call discardSomeReadBytes() on their buffers and a user can override this behavior easily. For example, ReplayingDecoder.discardInboundReadBytes() looks like the following:

    @Override
    public void discardInboundReadBytes(ChannelHandlerContext ctx) throws Exception {
        ByteBuf in = ctx.inboundByteBuffer();
        final int oldReaderIndex = in.readerIndex();
        super.discardInboundReadBytes(ctx);
        final int newReaderIndex = in.readerIndex();
        checkpoint -= oldReaderIndex - newReaderIndex;
    }

If a handler, which has its own buffer index variable, extends ReplayingDecoder or ByteToMessageDecoder, the handler can also override discardInboundReadBytes() and adjust its index variable accordingly.
Add ByteToMessageCodec.isEncodable()
Make ByteToMessageCodec.isEncodable() public like other similar methods
Rename MessageToMessageEncoder.freeInboundMessage() to freeOutboundMessage()
Make all encoder/decoder methods overridable in MessageToMessageCodec
Add missing codec operations in ByteToMessageCodec
Add missing decodeLast()
No need to override ByteToMessageCodec.decoder.discardInboundReadBytes()
Delegate to the actual encoder/decoder if possible
Fix checkstyle
[#902] Remove usage of generics for output of Encoder/Decoder to make them more flexible again
Simplify DefaultChannelPipeline
Fix DefaultChannelPipeline.toString() / Remove unnecessary conditions
Fix a bug where prev/next context is not always set
Remove unnecessary parameters
Do not read if a channel is inactive
Revert mistakenly committed test change
Fix inconsistent module name
[#561] [#912] Add Rxtx transport