Performance improvements and backpressure controls.

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.

examples/monitor.js

@@ -1,4 +1,4 @@
-var client  = require("redis").createClient(),
+var client  = require("../index").createClient(),
     util = require("util");
 
 client.monitor(function (err, res) {