Simply and speed up command argument processing logic.
Commands now return the true/false value from the underlying socket write(s).
Implement command_queue high water and low water for more better control of queueing.
* connection error did not properly trigger reconnection logic [GH-85]
* client.hmget(key, [val1, val2]) was not expanding properly [GH-66]
* client.quit() while in pub/sub mode would throw an error [GH-87]
* client.multi(['hmset', 'key', {foo: 'bar'}]) fails [GH-92]
