EventLogger: Implement log file opening.
util: Constify Datagram's getter functions and DatagramIterator's Datagram member.
Datagram: Add constructor to make a Datagram from a buffer+length.
EventLogger: Implement UDP packet receiving.
EventLogger: Log inbound packets to the log file.
EventLogger: Log when the Event Logger starts.
EventLogger: Add (unused) cycle_log function to cycle to a new log file.
EventLogger: Don't quote just because a column contains '_'.