• Finalize the Java APIs.

• Make sure the functionalities of Java part are enough to distribute a Java SDK:
  1. Make sure that pure Java users can run local mode and cluster mode with a single Jar.
  2. Run the benchmarks and stress tests of Java part.
  Note that we don't support cross-language calls in this version. That means cross-language-calls feature is an experimental feature now. (This should be supported in next several versions.)

• Bump Java version to 0.8.0 and freeze the merging operations until bumping to 0.8.1-SNAPSHOT.

ps: We should release Java part with the major releasing-process of Ray. That means for the next releasing of Ray, we should release wheel, and maven jars both.

After this release, I think we should improve our Java document as well. This seems an important issue for pure Java users now.

@ericl @raulchen @kfstorm Please point out if I missed some thing.