Improved Syslog Parsing

Anyone that dealt with Syslog knows that the format specification is a "goal". It's very common for formats to deviate slightly. To account for this we've updated our Syslog parsing to follow the RFC 3164, RFC 5424, and other common formats. With these changes Vector is very likely to parse a Syslog format, or anything like it. And, as always, if Vector's syslog source fails to parse your format you can always use the socket source and the regex_parser transform to roll your own collection parsing pipeline.