Provide cross platform utilities for process creation

This may go into trond's Platform package one day. But this is meant to
be a means to redirect output and "asynchronously" spawn processes on
both Unix and Windows platforms

Change-Id: Ie8c8a9db5720093e8454b538b2eaa33a01a0a4b8
Reviewed-on: http://review.couchbase.org/28007
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>