[Java] Improve the Java Doc of RocksObject

Summary:
Improve the Java Doc of RocksObject, which explains more about the life-cycle
of a native handle.

Test Plan: no code change

Reviewers: haobo, sdong, ankgup87

Reviewed By: ankgup87

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19179
[Java] Add HISTORY-JAVA.md and include both C++ and Java history files in .jar.

Summary:
Add HISTORY-JAVA.md and include both C++ and Java history files in .jar file
that describes important chagnes of RocksJava.

Test Plan: make rocksdbjava and make sure HISTORY.md is inside the .jar file

Reviewers: haobo, sdong, ankgup87

Reviewed By: ankgup87

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19185