Merge pull request #134 from tbak/master

Add README.md to ribbon module (proxy section only).
Make project compile under Java 8.

Most of the errors were coming from stricter rules for javadoc. Findbugs was upgraded
to version 3.0.0, and PowerMock to 1.5.4 to have Java 8 support.
Additionally gradle wrapper was updated to the latest 1.x version.