[development] Note that PHP arrays are fast

[Karoly Negyesi]

> * modulo is slower than bitwise-and and I think that this was the main culprit to the even/odd flip performance

But the patch was a bugfix and the race was between 

    $class = $class == 'even' ? 'odd' : 'even'

    $class = $flip[$class];

Because the key is not reliable, so we must flip the class.

> * microtimer is not a benchmarking tool

I know that the microtime is not accurate but -- what else if you need subsecond? Even the most ancient PCs had a 1/18.2 second timer, I am not intimate on newer designs.

Regards,

NK