Created retrolambda maven plugin. see issue #14

Hi, I created retrolambda-maven-plugin and it is now used in end-to-end-tests. Please review and merge if happy.

Seems to work ok and passes all tests. 

I left the dependency plugin and ant plugin combo commented out in end-to-end-tests/pom.xml for reference but I reckon it should be removed once you think the plugin covers the necessary use cases.

I've updated README.md but outstanding is still to put the plugin documentation somewhere. Running mvn clean site in retrolambda-maven-plugin generates the documentation for the plugin in target/site. I put stuff like that in a script like [this](https://github.com/davidmoten/rxjava-jdbc/blob/master/generate-site.sh) so I can update it easily. You'd have to setup the orfjackal.github.io repo to facilitate that. GitHub doco tells you how if you haven't got one already.

Cheers
Dave