[slf4j-dev] Prepared branch for slf4j 2.0

Hi Ceki I prepared the branch for slf4j 2.0. I cannot make a PR that targets a non existing branch: can you make one? Code is available at https://github.com/ffissore/slf4j/tree/2.0.0-SNAPSHOT I've replaced occurrences of java 1.5 and 1.6 to 1.8 and I've included slf4j fluent Let me know what you think federico