Add methods for using netty 4.1.x

[jmacleod]

Hey, I have a project I am working on where I have another dependency that uses netty 4.1.x. When I run it I get runtime errors that seem to be because netty-rest is uses netty-4.0.x.

It looks like I just needed to add the methods in this PR to make it work with netty-4.1.x. I have not done much developing in java so I am sure this isn't the right way to do it, but if you are willing to give me some guidance and think this might be worthwhile, I am willing to do the work.

I don't expect this is a mergable PR, so please reject it at your convenience.

Thanks!

[buremba]

@jmacleod the PR is great but I personally did not test the Netty version that you used in this PR. Once I wrote enough unit tests to cover the edge cases, I will merge your PR. Thanks a lot for the contribution!

[ratcashdev]

Is this project still active? What is the status of the Netty 4.1 upgrade?