Add option to configure stdio of php server process

[awhatley]

Several people (myself included) have expressed a desire to control the verbosity of the output of the php built-in server process, which by default logs all resource requests to stdout.

This pull request simply surfaces the lower-level spawn option for stdio, allowing stdin, out, and err to be independently configured as documented here: https://nodejs.org/api/child_process.html#child_process_options_stdio

Personally, I just set it to 'ignore' :-)

[thijskaspers]

Yes please! Every single webrequest is being logged by the php server, bloating the terminal. This is an easy fix for that by adding an extra option for the user.