Redis pipeline support, fixed commands and tests.

Hi,
Overview of changes I made:
    - Redis pipeline support (http://redis.io/topics/pipelining) with tests and updated README
        * modified client.py
        * added pipeline.py
        * added test_pipeline.py
    -  Fixed 'unknown command' error for commands: client_kill, client_list, config_get, config_resetstat, config_set, debug_object, debug_segfault, script_exists, script_flush, script_kill, script_load and 'args' name conflict for commands: eval, evalsha
        * modified gen_commands.py
        * regenerated commands.py
    - Fixed test_client.py and test_handler.py to also work with python3