Data Export and New Error Codes (v8.1.0)

The main feature in this release is the option of exporting received load traffic metadata (sequence numbers, timestamps,...) in CSV format. See README for feature details.

Also in this release, the ErrorStatus values used in the JSON output have been made much more granular (instead of just 1 for warning and -1 for error). Now, warnings are allocated values starting at 1 (one) - although only a handful are currently used. Error values start at 50 and can go up to a maximum of 255 (see udpst.h for details). Additionally, an ErrorMessage2 text field was also added to better communicate the cause-and-effect relationship between typical message pairs.