Modified PhpArray config writer to generate better readable array format.

Saw [this Twitter conversation](https://twitter.com/spiffyjr/status/388726534673928192) and agreed.

This PR modified `Zend\Config\Writer\PhpArray` to generate better readable arrays. Specifically, it will (1) indent 4 spaces per level instead of 2 and (2) put the opening `array(` on the same line as the `=>`.

Tests pass, and this "shouldn't" affect BC because it's "just" whitespace.