Implemented newrelic-daemon to be observed via 'heroku logs'

The newrelic-daemon is a spawned process, invoked by the PHP agent, which is truly daemonized (i.e., it is disassociated from the controlling TTY and running in the background). Therefore, the daemon is configured to write its log output to a file instead of to STDIO.

This change enables observation of the newrelic-daemon logs via 'heroku logs'.