Zadd map fix

Hi,
I would like to contribute this fix to Jedis.
The fix is about zadd method. Current jedis interface doesn't allow to add multiple member with the same score to an ordered set. This is a semantic limitation respect to ZADD Redis server command. The problem is the nature of the map that Jedis is accepting in the method signature to add multiple members at once. 
I've forked Jedis and created a branch called zadd-map-fix where I've coded a fixed version of the zadd called zaddFixed. I've also added a test called ZaddCommandTest where I've coded a first test that explains the problem and a second test that shows the solution. The test is running properly with "make test" command. 
The fix is quite simple but requires a change in the zadd signature.
Look forward hearing from you

Filippo